Download stratigraphy and history of raton basin and notes on san luis basin

BULLETIN OF THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS
VOL. 49. NO. II (NOVEMBER, 1965). PP. 2041-2075. 8 FIGS.
STRATIGRAPHY AND HISTORY OF RATON BASIN AND NOTES ON
SAN LUIS BASIN, COLORADO-NEW MEXICO1
ELMER H. BALTZ2
Albuquerque, New Mexico
ABSTRACT
Raton Basin.—The Raton basin of northeastern New Mexico and southeastern Colorado is
a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by
the Wet Mountains uplift and Apishapa arch, and on the east by the Sierra Grande arch. The basin
is asymmetrical and the northerly trending axis generally is near the Sangre de Cristo uplift. The
jntrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from
the shallower, southern, Las Vegas sub-basin.
During most of Paleozoic time the Raton basin and its bounding uplifts were part of the
relatively stable "continental backbone." The oldest known sedimentary rocks in the basin are
marine beds of Devonian( ?) and Mississippian age. In Early Pennsylvanian time the Rowe-Mora
and Central Colorado geosynclinal basins were formed in the area of the present Sangre de Cristo
uplift and the western half of the present Raton basin. The basins were bounded on the west by
the intermittently rising San Luis uplift, and on the east and north by the ancestral Sierra Grande,
Apishapa, and Wet Mountains uplifts. A mainly marine unstable shelf facies of the Magdalena
CJroup of Pennsylvanian age in the Las Vegas sub-basin is 1,500-2,500 feet thick. These rocks
•_-rade abruptly northward into a marine geosynclinal facies which is as much as 6,000 feet thick in
the Las Vegas sub-basin. The Magdalena Group is absent from the Cimarron arch, but it probably
is present in the western half of the northern Raton basin where it may be 4,000 feet thick.
Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was
derived mainly from the San Luis uplift, filled the Rowe-Mora and Central Colorado basins,
and lapped onto Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-9,500 feet thick at the north.
Higher Permian rocks, and Upper Triassic and Upper Jurassic rocks have average aggregate
thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed
the region of the present Raton basin and buried the late Paleozoic, Sierra Grande, and Apishapa
uplifts. Cretaceous marine shale interbedded with some sandstone blanketed the entire region. The
Cretaceous rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas subbasin are 900-1,000 feet thick.
The terrestrial latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in
aL'u'regate maximum thickness in the northern part of the Raton basin, were derived mainly from
the rejuvenated San Luis uplift. During early and middle Tertiary time, the San Luis uplift and the
western parts of the Paleozoic Rowe-Mora and Central Colorado basins were elevated to form the
Sangre de Cristo uplift. The present Raton basin, Wet Mountains uplift, and the Apishapa, Las
Animas, and Sierra Grande arches were formed in early Tertiary time.
The Raton basin has been a basinal area for most of its history since Early Pennsylvanian time.
Thick marine sediments of Pennsylvanian and Cretaceous ages probably were sources of petroleum.
Potential traps, both stratigraphic and structural, are known to exist in many parts of the basin,
although these traps are mainly untested. Encouraging "shows" of oil and gas have been found
in Pennsylvanian rocks in the Las Vegas sub-basin, and in Cretaceous rocks in several parts of the
basin, but there has been no commercial production.
San Luis Basin.—In middle and late Tertiary time the ancient San Luis uplift was tilted eastward and its eastern part foundered to form the San Luis basin, which is the northern part of the
complex Rio Grande trough. The northwestern part of the San Luis basin merges into the eastern
flank of the San Juan Mountains uplift. The southwestern part of the basin is bounded by the easttilted Brazos uplift. The eastern and northern boundaries of the basin are a complex fault zone
along the western margin of the Sangre de Cristo uplift which merges, around the northern end
of the basin, with the Sawatch and Gunnison uplifts.
Much of the San Luis basin is filled with middle to upper Tertiary and Quaternary
terrestrial sediments and interbedded andesite and basalt that are at least 5,000 feet thick locally.
This basin fill rests on lower and middle Tertiary volcanics that are related to the volcanics of
the San Juan Mountains. Because the region of the San Luis basin was a part of the Paleozoic and
Mesozoic San Luis uplift, it is doubtful that extensive areas of Paleozoic or Mesozoic rocks are
preserved beneath the lower to middle Tertiary volcanics. The stratigraphy and geologic history
of the San Luis basin are not encouraging for petroleum possibilities.
q
a
I
•fi
1
1
Read before the Rocky Mountain Section of the Association at Durango, Colorado, September 29,
'°t>4. Manuscript received, July 15, 1965. Published by permission of the Director of the United States
ieological Survey.
'Geologist, Ground Water Branch, United States Geological Survey.
2041
ELMKR H. BALTZ
2042
INTRODUCTION
The Raton and San Luis basins of Colorado
and New Mexico have attracted only slight attention from the petroleum industry, even though
the first wildcat test in the Raton basin region
was drilled almost 65 years ago. There has been
no commercial production of petroleum in either
basin, but encouraging "shows" of oil and gas
have been found in several rock units at widely
scattered points in the Raton basin.
The subsurface geology of both basins is poorly known because of the scarcity of deep test
wells. However, a general reconstruction of the
distribution of rock units in the basins can be obtained by comparing subsurface data with the
somewhat better-known surface geology of the
basins and their bounding uplifts. This approach
is not without its problems, because Cenozoic
structural complications on the margins of the
basins and in the uplifts cause considerable doubt
about the distribution and thickness of some stratigraphic units. The reconstructions derived from
combining surface and subsurface geology indicate considerable stratigraphic complexity in the
Raton and San Luis basins. In the Raton basin
this complexity probably favors the occurrence of
petroleum deposits; in the San Luis basin, the
complexity appears to be unfavorable.
RATON BASIN
GENERAL TECTONIC DESCRIPTION
The Raton basin of southeastern Colorado and
northeastern New Mexico is the southernmost of
the Laramide intracratonic folded basins at the
eastern margin of the Rocky Mountains (Fig. 1).
The northernmost part—the Huerfano Park region—is intermontane, but most of the basin lies
in the western part of the Great Plains. Throughout its length the Raton basin is bordered at the
west by the Sangre de Cristo uplift. At the east
the basin is bordered by the broad, low, and locally ill-defined Sierra Grande arch. The northeastern boundary is the Wet Mountains uplift
and its structurally lower southeastward continuation, the Apishapa arch. The structural basin
thus delineated is about 175 miles in northsouth length. Its greatest width is about 65 miles
near the New Mexico-Colorado line.
Within the Raton basin is the low northwesterly trending Cimarron arch, named for the Cimar-
ron River, which lies on or near the arch bclwtn
the vicinity of Ute Park and Springer, New Mti
ico. East of Springer the intrabasinal arch mtrjn
with the Sierra Grande arch. In older rt|»ni>
(Darton, 1928, p. 314) the terms Raton ba-in or
Raton coal basin were applied only to the Ian.-;:
and structurally deeper part of the basin north <,!
the Cimarron arch, whereas the shallower suuit.
ern part was called the Las Vegas basin. Hut
ever, more recently (Johnson and Wood, N ; t
Fig. 1; Gableman, 1956, p. 35; Baltz and Real
1959, p. 2) the term Raton basin has been a|>
plied in the broader sense to the entire region \<
tween the Sangre de Cristo uplift and the Sinn
Grande and Apishapa arches, and the northm.
part of the basin is considered to merge, aun : >
the Cimarron intrabasinal arch, into the southti:.
basin. It is in this broader sense that the tern,
Raton basin is used in the present report. 'll«
term Las Vegas sub-basin is applied to the part i,i
the Raton basin south of the Cimarron intraha-i
nal arch. The main part of the basin that Innorth of the arch is called simply the northun
Raton basin.
Most of the Sangre de Cristo uplift west of ihr
Raton basin is composed of crystalline rocks u!
Precambrian age and sedimentary rocks Itui
range in age from Ordovician to Early Permian
These rocks were uplifted and crowded eastward
by Laramide orogenic forces. The western linil.
of the basin northward from Las Vegas is, ai
most places, vertical or overturned, and generalk
is broken by west-dipping high-angle reverM
faults and thrusts (Northrop and others, 194t>,
lialtz and Hachman, 1956, p. 104-107; liachnian.
1953; Wanek and others, 1964; Dane and Bathman, 1962; Johnson, Wood, and Harbour, l'J5.>
liolyard, 1959). In Huerfano Park low-angle imbricate thrust plates extend well into the western
part of the basin (Burbank and Goddard, 193;,
Johnson, 1959, p. 107-111). Igneous rocks of Tertiary age occur as sills, dikes, and stocks alun:
the western margin of the basin in the vicinity u!
Ute Park and Eagle Nest, and west and souihwest of Huerfano Park.
The Raton basin is an asymmetrical downwarp
complementary to the Sangre de Cristo uplift
and, except in the vicinity of the Cimarron ardi.
the axis of the structural trough lies in the WKIern part of the basin. North of the Spanish Peaks
the axis of the basin bifurcates around a souih-
RATON AND SAN LUIS HASINS
20-43
U
RATON AND SAN LUIS BASINS
2044
2045
ELMER H. BALTZ
plunging spur (Greenhorn anticline) of the Wet
Mountains uplift. The western axis has been called
the La Veta syncline, whereas the eastern axis
is the Delcarbon syncline (Johnson and Stephens,
1954). The Tertiary igneous stocks of the Spanish Peaks were intruded in the trough of the
northern part of the basin, and are accompanied
by a swarm of large dikes that occur in a broad
east-west band which extends nearly across the
basin north of Trinidad, Colorado (Johnson,
1961).
The eastern limb of the Raton basin is very
broad and dips very gently west from the Sierra
Grande arch and southwest from the Apishapa
arch. For convenience, on Figure 1 the flanks of
the arches are included in the basin, although it
could be debated at great length where the eastern limb of the basin ends and the western limbs
of the arches begin. The Huerfano Park segment
of the basin is separated from the Wet Mountains uplift by large faults downthrown to the
west (Johnson, Wood, and Harbour, 1958; Johnson, 1959).
The Sierra Grande arch has two main culminations (Foster and Stipp, 1961), one east and
northeast of Springer, New Mexico (Wood, Northrop, and Griggs, 1953), and the other east of
Las Vegas. The culminations are separated by a
broad, flat saddle on the northeastern margin of
the La.s Vegas sub-basin. The Apishapa arch is a
broad, wrinkled, and slightly faulted saddle that
merges into the northern part of the Sierra
Grande arch (Doeringsfeld, Amuedo, and Ivey,
1956; Oborne, 1956, p. 61-62).
The general configurations of the troughs of
the Las Vegas sub-basin and the northern part of
the Raton basin are shown in Figure 2. In most
of the Las Vegas sub-basin and on the Citnarron
arch the surface rocks are Cretaceous. Rocks of
Jurassic, Triassic, and Permian ages are exposed
at the western margin of the basin and in the
central parts of Ocate anticline and Turkey
Mountain dome. The maximum aggregate thickness of sedimentary rocks in the Las Vegas subbasin is of the order of 12,700 feet (section li-B',
Fig. 2). The Magdalena Group of Pennsylvania!]
age, and the Sangre de Cristo Formation of Pennsylvanian and Early Permian age are as much as
8,800 feet thick in the trough of the basin, but
these rocks thin eastward toward the Sierra
Grande arch and, on the eastern limb of the
basin, the Magdalena Group is absent. There are
too few deep wells for accurate delineation of thr
wedge-edges of various stratigraphic units, lite
the data are sufficient to show (sections A-A' ai,:
li-B', Fig. 2) that the wedge-outs do occur.
North of Ute Park, New Mexico, upper Crtu
ceous and lower to middle Tertiary rocks furc
the surface of most of the northern Raton basil
The aggregate maximum thickness of sedimenUr;
rocks in the trough of the northern part of Ib:
basin is of the order of 25,000 feet. Howevti.
this figure is misleading because of anjtulu
unconformities and overlaps within the Tertian
rocks and because Quaternary erosion has it
moved large amounts of rocks from parts (if thr
basin. Perhaps no more than 16,000-20,000 fen
of sedimentary rocks are preserved at any plaic
in the trough. No wells have reached the Precambrian in the trough of the northern part of thr
Raton basin. However, Pennsylvanian and Lowrr
Permian rocks are known to be 13,000-15,01
feet thick in the Sangre de Cristo uplift, and thin
or absent on the eastern flank of most of thr
basin (section C-C', Fig. 2), as in the Las \\(jsub-basin. Similar relations obtain also in itu
Huerfano Park area (Johnson, 1959, espedallv
pi. 6).
PALEOTECTONICS
The latest Cretaceous and Tertiary tectonic
elements of the Raton basin region are related li
major structural features that were formed mainly in Pennsylvanian and Permian time. These an
cient features are shown in generalized form MI
Figure 3. The San Luis uplift at the west was thr
southeastern part of a large Paleozoic and earK
Mesozoic positive area that extended northwcM
ward across southwestern Colorado. This pnsiiiu
area, in its entirety, is generally called the I'ncompahgre uplift or geanticline (see Kin;;, 14 ; g
p. 104-105). The eastern margin of the San Luj.
uplift seems to have been mainly in the area thit
is now the downfaulted San Luis basin, which \the northern segment of the present Rio (iranil
trough. The southwestern and central parts of thr
ancient San Luis uplift are in the Laramide Brazos uplift and beneath the San Juan Mountainvolcanic field (Fig. 1) (see Read and othi-i.
1949; Dane, 1948).
The area of the present southern Sangre ilr
Cristo uplift and the Las Vegas sub-basin \u-it
the site of a geosynclinal basin—the Rowe-Mura
basin (Read and Wood, 1947, p. 225-227)—whiih
by between the ancient San Luis uplift and the
ancestral Sierra Grande uplift (so called to distinguish it from the present Sierra Grande arch).
The Rowe-Mora basin was connected at the south
hy a low, folded saddle with the ancestral Tucumcari basin. The area of the northern Sangre
de Cristo uplift and probably much of the northtin Raton basin were parts of the Central Colorado basin that was enclosed between the San
Luis uplift and the ancestral Wet Mountains-Apishapa uplift. The Central Colorado basin probalily was connected with the Rowe-Mora basin in
Early and Middle Pennsylvanian time. However,
scanty and problematic stratigraphic evidence
seems to indicate that the ancestral Cimarron
arch arose as part of the Sierra Grande uplift in
Middle and Late Pennsylvanian time to separate,
at least partly, the two geosynclinal basins.
ROCKS OF r i E V O N I A N ( p ) AND MISSISSIPPIAN
pian ages crop out in the northern Sangre de
Cristo Mountains (Litsey, 1956), but these rocks
wedge out southward at outcrops and may not be
present in the subsurface of the northern Raton
basin.
During much of Paleozoic time the region including the present Sierra Grande and Apishapa
uplifts, Raton basin, and much of the Sangre de
Cristo uplift seems to have been part of the
broad, southwest-trending, shelf-like "continental
backbone" (King, 1951, p. 30), on which sedimentary rocks older than Devonian are not present. Whether pre-Devonian sedimentary rocks
were deposited on and later eroded from this
shelf is a matter of conjecture. Maher and Collins (1949) indicate that the thick pre-Pennsylvanian, Paleozoic sequence of Kansas, Oklahoma,
and eastern Colorado thins toward the Sierra
Grande uplift in a manner suggesting that it has
a long history as a positive area.
AOES
The oldest sedimentary rocks known to be present in the Raton basin are marine sandstone and
ilolomitic limestone of the Espiritu Santo Formation of Devonian(P) age (Fig. 4). This unit
ranges from a few feet to 80 feet thick in the
southern Sangre de Cristo Mountains (Baltz and
Read, 1960, p. 1754-1756), and is about 35 feet
thick at the Continental No. 1 Leatherwood-Reed
well (no. 1, Fig. 4) in the Las Vegas sub-basin.
The Espiritu Santo probably correlates with the
Chaffee Formation of Late Devonian age in the
northern Sangre lie Cristo Mountains.
The Tererro Formation of Mississippian age
rests unconformably on the Espiritu Santo and is
composed of limestone breccia and marine conglomerate, clastic, and crystalline limestone, and
siltstone. The Tererro ranges in thickness from a
few feet to 130 feet in the southern Sangre de
Cristo Mountains (lialtz and Read, 1960, p.
1760) and from 50 to possibly more than 100
feet in the Las Vegas sub-basin. The breccia and
conglomerate units of the Tererro are porous at
some outcrops, and were a lost-circulation zone in
the Continental No. 1 Mares-Duran well on Ocate
anticline, indicating some porosity and permeability in the subsurface also. Although the Tererro
is below possible source rocks, it nvght be a petroleum reservoir under favorable structural conditions on the flanks of the Las Vegas sub-basin
or near faults in the basin.
Rocks of Ordovician, Devonian, and Mississip-
ROCKS OF PENNSYLVANIAN AGE
The first recorded stage of formation of the
Raton basin was in Early Pennsylvanian time
when the orogenic forces that produced the Ancestral Rockies began to downwarp the RoweMora and Central Colorado basins. The Magdalena Group and the Minturn Formation, both of
Pennsylvanian age, and the Sangre de Cristo Formation of Pennsylvanian and Permian age (Fig.
4) are complex suites of sediments whose vertical
and lateral variations reflect several stages of formation and eventual filling of the geosynclinal
basins.
Magdalena Croup and Minturn Formation.—
The Magdalena Group in New Mexico consists of
the Sandia Formation and the overlying Madera
Limestone. The Sandia Formation (Atoka age),
the lower unit of the Magdalena in the southern
Sangre de Cristo uplift and the Las Vegas subbasin, is a suite of coarse-grained to conglomeratic sandstone, dark gray shale, and subordinate
thin limestone beds deposited in a mixed marineterrestrial environment during a general transgression of the Pennsylvanian seas. The Sandia is 300-1,600 feet thick in the Las Vegas subbasin. The Deer Creek Formation of Bolyard
(1959, p. 1904-1910) in the northern Sangre de
Cristo Mountains is a similar sequence of rocks
that contains red shale and correlates generally
with the Sandia. The Deer Creek may correlate
with the lower part of the Minturn that lies at
Spanish Peaks
(north of section)
EXPLANATION
Nort hern
Raton
basin
The
Huerlano and Cuchoro Fms
TKpr
Poison Canyon and Raton Fms
Kvt
Vermejo Fm. and Trinidad Ss
Kpn
Pierre Sh , Niobroro Fm., Carlile Sh,
Greenhorn Ls , and Groneros Sh.
Kdp
Dakota Ss. and Purgatoire Fm
m
lS
r-S
Morrison, Ralston Creek (?), and Entrada Fms.J cc u
T -* S
15
Precambnan c r y s t a l l i n e
Dockum Group
r*
j ._ *
P
Bernol, Son Andres, Glorieta, and Yeso Fms.
PP»c
Songre de Cristo Fm.
Pm
Maadolena Group
O c a t e anticline
Precambrian crystalline
rocks
List of wells
A
Sangre de
Cristo uplift
Las
Vegas
sub-basin
Sierra Grande
arch
Colorado
(T) Shell/ Oil Co no.I ColOfOdo Fu«i and Iron Co.. sec. 29, T. 34S..R.6S W.
(2) Continental Oil Co no I Colorado Fuel ond Iron Co..sec.l3,T34S..R.66W
Stanolind Otl and Got Co no.) Colorado Fuel arid Iron Co. sec. 31,
T. 34S-. R 63*.
New Metico
© Cont.nental O.I Co nol Mores-Duron.sec. 14, T.23 N..R.I7 E
(5) California Co. no I Floerscheim. SSC.I5, T. 23N., R. 24 E.
©Cant
Tererro ond
Etpirltu Sonto Fms.^.
(Miuissippicm ond
D«vonion(?))
IMO. 2.—Diagrammatic crew, sen,
Mi
„( Raton basin.
ELMER H. BALTZ
2048
z
o
s
•« LJn ~
Q.
X
S o
c o
£ E
RATON AND SAN LUIS BASINS
Ihe north (Uolyard, p. 1909). The Deer Creek
ranges from 300 to 1,100 feet thick.
The Madera Limestone (Atoka through Virgil
age) in the southern Sangre de Cristo uplift
(Read and others, 1944; Read and Wood, 1947,
Fig. 1) and the Las Vegas sub-basin consists of a
lower, gray limestone member and an upper, arkosic limestone member. The gray limestone
member is composed of interbedded crystalline
fussiliferous limestone, dark gray shale, and
sandstone, and is 700-1,200 feet thick. The arkosic limestone member consists of interbedded
crystalline and clastic limestone, red, green, and
gray shale, and conglomeratic arkosic sandstone,
and is 450-2,770 feet thick. The gray limestone
member was deposited in a predominantly marine
environment, whereas the arkosic limestone member was deposited in a mixed marine-terrestrial
environment and records strongly accelerated orogeny in the geosynclinal area and its bounding
uplifts.
Rocks of Des Moines age in the Colorado part
of the Sangre de Cristo uplift have been called
Ihe Madera Formation by Brill (1952, PI. 1 and
p. 816-820) and Bolyard (1959, p. 1910-1918).
These writers applied the terms "gray limestone
member" and "arkosic limestone member" to
rocks which are lithologically somewhat similar to
the members of the Madera in New Mexico, although the arkosic limestone member of Brill and
Bolyard is, for the most part, older than the arkosic limestone member of New Mexico. The
Madera of these writers is 2,200-2,400 feet thick.
Brill applied the name Whiskey Creek Pass Limestone Member to a thin unit which is the
upper part of his Madera Formation in Colorado,
and he extended the term also into New Mexico.
However, the Whiskey Creek Pass Limestone in
Colorado is said to be Des Moines in age, whereas
the youngest rocks of the Madera in northern
New Mexico contain fusulinids of Virgil age.
The Deer Creek and Madera Formations of
Bolyard and Brill grade northward, in the Sangre
de Cristo uplift northwest of Huerfano Park, into
a thick sequence of interbedded, brown, gray, and
yellow conglomerate, arkosic sandstone, shale,
and thin limestone of the Minturn Formation
(Atoka(?) through Des Moines age; Bolyard,
1959, p. 1919-1922). These rocks contain a few
thin marine beds, but were deposited as a dominantly fluviatile facies in a part of the Central
Colorado basin that must have been near moun-
2049
tainous highlands. The Minturn is more than
5,300 feet thick.
The total thickness of the Magdalena Group of
New Mexico and its general equivalents in Colorado is shown in Figure 5. This map relies heavily on surface data from the Sangre de Cristo
uplift because so few wells have been drilled to
the Precambrian basement in this region. Most of
the basement tests on the eastern flank of the
Raton basin and on the Sierra Grande uplift were
drilled on surface anticlines. Possibly some of
these anticlines are rejuvenated Paleozoic folds;
or, they might have resulted partly from
differential compaction and "draping" of the
sedimentary rocks across old highs. If this is the
case, northwesterly aligned synclinal basins containing Pennsylvanian rocks might be present ar,d
undetected at places on the eastern limb of the
basin and on the uplift.
The interpretation of the distribution of the
Magdalena Group along the northern and southern flanks of the Cimarron arch is complicated,
not only by a lack of subsurface control, but also
by structural complications at the eastern side of
the Sangre de Cristo uplift. West of Eagle Nest
faulted slices of the Magdalena are several thousand feet thick. However, Wanek and others
(1964) indicate that the Sangre de Cristo Formation lies on Precambrian rocks at outcrops south
and west of Ute Park, and Triassic rocks lie on
Precambrian rocks near the dam at Eagle Nest.
Wanek and Read (1956, p. 92) interpret this
contact at Eagle Nest to be a relatively flat, westdipping fault downthrown on the west. C. B.
Read (oral communication, 1965) indicates that
the contact of the Sangre de Cristo and Precambrian rocks east of Eagle Nest also may be
faulted. The eastern margin of the Sangre de Cristo
uplift south of Ute Park is bounded by a large
fault downthrown on the east (Wanek and
others, 1964). Thus, according to C. B. Read, the
bulge in the eastern front of the Sangre de Cristo
uplift southeast of Eagle Nest may have been a
result of Laramide upward movement of a mass
of Precambrian granite which was completely
bounded by faults, and which pierced and shoved
aside part of the overlying sedimentary rocks. A
possible alternate explanation is that the Laramide deformation postulated by Read may have
occurred on a Paleozoic positive area, as depicted
in Figures 3 and 5.
North of Eagle Nest along the eastern margin
2050
ELMER H. BALTZ
SOUTH
Southern Raton basin
(Las Vegas sub-basin)
©
Eagle Nest area
(Cimarron arch)
N.M&lo.
NORTH
Northern Sangre de Cristo Mtns.
Scale
(feit)
©
©
- 15,000
Datum- Top of Songrt de Cristo Formation
Crestone
Sangre de Cristo Formation
/ v
member
, , -1 '
/ P -<;
Cristo
', •> '- •- _
Formation
" l ' i s' J'/ -
/ - _ o. o
Precambrian x
crystalline rocke ', ^'
/
-
X X
'
Whiskey Creek Pass
Limestone Member
of Brill (1952)
Terrero and Espiritu Santo^il-'c
s v
Formations
(Mississippian and Devonian!?))
Arkosic
limestone member
Sources of d o t o •
(?)
Continental Oil Co no. I Leo t her wood - Reed well. sec. 15, T 16 N , R, 17 E.
©
HoncocK E.plor Co. no. I S e d b e r r y well, sec 25. T 1 7 N . R . I 6 E .
(4)
Conlmental Oil Co. no. I M a r e s - D u r o n well, Ocote anticline, sec. 14. T 2 3 N , R 17 E.
(?)
O u t c r o p s near Eagle Nest ( W a n e k ond Read, 1956, p. 9 0 - 9 2 ) , outcrops in C.morron C r e e h Canyon
C r e e < F o rm a t i o n
^6er
Bolyard
(1959)
'/-* ^
© s-,,
(7)
Su.f
®
Su,f
tig.aphic section, W h i s k e y C r e e k Pan I Brill, 1952, p 828 - 8 2 9 - , Bolyard.1959. p 1900)
8o
Solyord,
1959, p 1900, 1912. 1914 )
S
2051
RATON AND SAN LUIS BASINS
Surloc
SuXoc
1 9 2 4 - 1 9 2 6 , Brill, 1952, p
' /N
id. 1959. p
1900
)
Length of diagram n obw*
Line of diagram it ir,u«
E H eolli.1965
FIG. 4.—Diagram shim in ntlations of Paleozoic rocks.
Mississip"pian~i
and older sedimentary rocks-^x.
2052
ELMER H. BALTZ
c
RATON AND SAN LUIS HASINS
+- «
.S c
W 3 •*" *- "*~ ^-~
iO O « O ^
nfI
I j
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of the Sangre de Cristo uplift Precambrian rocks
are in fault contact with the Sangre de Cristo
Formation at least as far north as the State line
(A. A. Wanek, oral communication, 1QS8). Here,
and in the adjacent part of the Raton basin, it is
impossible to say whether the Magdalena Group
is present. The Union Oil Co. Nos. 1 and 2 Bartlett wells drilled on Vermejo Park anticline (Fig.
1) reached total depth in igneous rocks that
occur in the lower part of the Cretaceous section.
I These wells have been interpreted as possibly
having reached the Precambrian (Foster and
Stipp, 1961). However, this seems unlikely because the Sangre de Cristo Formation and overlying Permian, Triassic, and Jurassic rocks are present below the Cretaceous at outcrops west of
Vermejo Park dome (loc. 7, Fig. 6) and in all the
other deep wells in this region, although farther
east the Sangre de Cristo is very thin. Bates
(1942, p. 145) suggests that the core of Vermejo
Park dome is occupied by an igneous intrusion,
presumably related to other Tertiary intrusives
cm the western margin of the basin. Thus, the
possibility that the Magdalena may be present in
(he subsurface is not eliminated. Recent drilling
shows that domal or laccolithic intrusions of Tertiary age occur in the Magdalena Group at Turkey Mountain dome in the Las Vegas sub-basin.
Outcrops indicate Tertiary laccolithic intrusives
also at Capulin and Rancho Grande anticlines on
the Sierra Grande uplift (Wood el al, 1953).
In the Colorado part of the basin the isopaihous lines are inferred only from thicknesses at
outcrops west of the basin and from the few
wells on the eastern limb of the basin that indicate the Magdalena is not present there (cross
section C-C', Fig. 2). Wells at a few places on
the Apishapa arch have found "shows" of oil in a
thin sequence of red shale, arkose, and thin limestone that has been called the "lower carbonate zone" of the Sangre de Cristo or the Fountain
Formation, and has also been assigned to the arkosic limestone member of the Madera Formation (Clair and Bradish, 1956a, b; Oborne,
1956). These rocks may lie east of the crest of
the ancestral Wet Mountain-Apishapa uplift
(Oborne, 1956, p. 63-64), and their relation to
the Magdalena Group or Sangre de Cristo Formation of the Sangre de Cristo uplift has not
been established with certainty. Along the western flank of the Wet Mountains uplift the Sangre
de Cristo Formation is known to thin and lap
2053
onto Precambrian rocks (Johnson, 1959, p. 93),
but a very thick section of rocks referable to the
Magdalena and the Minturn underlies the Sangre
de Cristo in the western part of Huerfano Park.
Fades.—At the southern end of the ancient
Rowe-Mora basin (Fig. 3) the Sandia and Madera Formations accumulated on an unstable,
mainly marine shelf (stippled on Fig. 5). The
Sandia Formation on the shelf contains numerous
thick, fairly clean sandstone beds. The Madera
contains many relatively thick biohermal limestones, some clastic limestones, and some relatively clean sandstones interbedded in shale. The
shelf facies is characterized by local inter- and
intraformational angular unconformities, and secondary porosity was developed on some of them.
Three large anticlines were formed on the shelf
in Pennsylvanian and Early Permian time.
The shelf facies can be projected eastward
from the mountains into the subsurface of the
Las Vegas sub-basin, although its northern edge
can not be located accurately from existing subsurface data. Asphaltic residues occur in faulted
outcrops of the Madera and Sangre de Cristo
Formations northwest of Las Vegas (Northrop
and others, 1946), and the Starr Adams No. 3
and Hancock No. 1 Sedberry wells on the Graham anticline north of Las Vegas encountered
strong "shows" of gas in the shelf facies of the
Madera. "Shows" of oil also have been reported
from the shelf facies of the Madera near the
southern end of the Sangre de Cristo uplift. To
date there has been no commercial production of
oil or gas.
The shelf facies of the Magdalena Group
thickens northward rather abruptly and grades
laterally into a mainly marine geosynclinal facies
(unpatterned on Fig. 5) in which thick gray and
black shale predominates over sandstone and limestone. Although the thick shale might have
been a source of petroleum, the sandstone and
limestone are generally argillaceous and impermeable. The Continental No. 1 Mares-Duran well
on Ocate anticline penetrated about 5,500 feet of
rocks of the geosynclinal facies without "shows"
of oil or gas. The facies of the Deer Creek and
Madera Formations in the northern Sangre de
Cristo uplift is similar to the geosynclinal facies
of the Las Vegas sub-basin. The fluviatile sandstones of the Minturn Formation might offer better possibilities for reservoirs.
2054
ELMER H. BALTZ
ROCKS OF PENNSYLVANIAN AND PERMIAN
AGE
Sangre de Cristo Formation.—The Sangre de
Cristo Formation is composed of thick red and
green shale with interbedded arkose and conglomerate and a few thin beds of limestone. Most of
the formation is terrestrial, but the lower third
contains a few thin tongues of marine limestone
(Zeller and Baltz, 1954, p. 3) in the southern
Sangre de Cristo uplift and Las Vegas sub-basin.
Thin non-marine limestone beds also occur at several positions in the formation. Surface work
northwest of Las Vegas determined that the
upper (Missouri and Virgil) part of the arkosic
limestone member of the Madera grades northward into the lower part of the Sangre de Cristo
Formation. This lower part, at least, of the
Sangre de Cristo seems to have been derived
from the north, probably from the ancestral Cimarron arch. Similarly, the overlying Yeso Formation of Permian (Leonard) age grades northward into the upper part of the Sangre de Cristo
(Bachman, 1953). Thus, the Sangre de Cristo,
which is as much as 3,500 feet thick in the Las
Vegas sub-basin, contains rocks ranging in age
from Late Pennsylvanian through Karly Permian.
In the northern Sangre de Cristo uplift and
western part of the northern Raton basin the
Sangre de Cristo Formation ranges from 6,500 to
at least 9,500 feet thick (lirill, 1952, p. 821).
Early Permian vertebrates have been found in
the Sangre de Cristo Formation, but it has not
been established whether the formation also contains rocks of Pennsylvanian age in Colorado. Thin
marine limestone was reported at one locality by
Holyard (1959, p. 1924). The lithologic character
of the Sangre de Cristo in Colorado is generally
similar to that in New Mexico, but northwest of
Huerfano Park the Crestone Conglomerate Member of Bolyard (1959, p. 1924) is 6,000 feet thick
and consists predominantly of massive boulder and
cobble conglomerate that probably was derived
from a nearby mountainous lerrane in the San
Luis uplift.
The Sangre de Cristo Formation is thickest in
I lie troughs of the ancient Kowe-Mora and Central Colorado basins. The formation thins eastward onto the Wet Mountains-Apishapa, Sierra
Grande, and Cimarron uplifts where it overlaps
the Magdalena Group and rests on Precambrian
rocks. On the Apishapa uplift Permian rocks res!
locally on pre-Pennsylvanian Paleozoic rocks. At
places on the uplifts the Sangre de Cristo is only
a few hundred feet thick and, locally on the Sierra Grande uplift, Triassic rocks rest on monadnocks of Precambrian rocks (Wood et al., 19531.
The influx into the geosynclinal basins of larnc
amounts of arkose and conglomerate of the upper
part of the Madera and lower part of the Sangre
de Cristo Formation in Late Pennsylvanian time
indicates a period of strong orogeny which continued through Early Permian (\Volfcamp) time.
The Sierra Grande uplift, Cimarron arch, am]
Wet Mountains uplift must have supplied a large
amount of the first-cycle detritus, but they were
mainly buried by the Sangre de Cristo Formation
in Early Permian time. The influence of the ancient San Luis uplift is difficult to evaluate because much of the uplift is now downfaulted intu
the Rio Grande trough, and much of the uplift is
concealed beneath the San Juan Mountains volcanic field. In the western part of the San Luis
uplift in New Mexico (the present Brazos
uplift), Permian rocks rest on the Frecambrian
and are overlapped by Triassic rocks. The San
Luis uplift seems to have supplied a huge amount
of the detritus which finally forced the sea out of
the geosynclinal basins, filled (hern, and lapped
onto the eastern u p l i f t s . The orogeny that culminated in Late Pennsylvanian and Early Permian
time was the most profound tectonic event recorded for the Raton basin region from Precambrian time to latest Cretaceous time. The tectonic
elements that were established in the late Paleozoic
influenced later sedimentation and geologic structure.
Although the Sangre de Cristo Formation does
not contain rocks that are likely sources of petroleum, some of the arkoses might be suitable reservoirs in areas where they overlap Pennsylvanian marine rocks on the margins of the Las
Vegas sub-basin and Cimarron arch and on the
eastern limb of the northern Raton basin. To
date these subsurface areas of overlap have not
been located or tested anywhere in the basin.
"Shows" of oil and gas in the Sangre de Cri^tu
were reported on the Graham anticline in New
Mexico, and asphaltic residues occur in the
Sangre de Cristo at outcrops northwest of Las
Vegas (Northrop and others, 1946).
RATON AND SAN LUIS BASINS
KUCKS OF PEKMIAN AGE
In the waning phases of Early Permian orogeny, the seas returned, covering part of the Raton
laiin region, and the Yeso Formation and Glorida Sandstone of Leonard age, San Andres Limestone of Leonard and Guadalupe age, and Bernal
Formation of Guadalupe age were deposited in
the region of the southern Sangre de Cristo
uplift, the Las Vegas sub-basin, and the southwestern Sierra Grande arch (Fig. 6). Similar
rocks are present also in part of the northern
Raton basin, and at places on the Apishapa arch.
Yeso Formation.—The Yeso Formation in the
Las Vegas sub-basin and southern Sangre de Cristo uplift consists of orange to brick-red siltstone
and shale, fine-grained sandstone, and local dolomite and gypsum. The Yeso is about 500 feet
thick at the south but thins northward and disappears south of the Cimarron arch (Brill, 1952, p.
827-828). Bachman (1953) pointed out that the
Sangre de Cristo and Yeso intertongue and the
Yeso is replaced laterally northward by the upper
part of the Sangre de Cristo Formation. This
may indicate that the Cimarron arch was supplying some detritus in Leonard time.
Glorieta Sandstone.—The Glorieta Sandstone
consists of gray, fine- to medium-grained, wellsorted, well-cemented, marine sandstone that is as
much as 275 feet thick. The Glorieta becomes
coarser-grained north of Ocate anticline and is
absent from outcrops at the southwestern margin
of the Cimarron arch (Brill, 1952, p. 828; Baltz
and Bachman, 1956, p. 101). Southward-inclined
imbricate bedding in the vicinity of Ocate anticline seems to indicate that the sediments of the
Glorieta in this area were derived from the north,
possibly from the Cimarron arch. Oil stains occur
at places in the Glorieta, but these rocks have
not yielded oil in the Raton basin. The Lyons
Sandstone of Colorado (probably equivalent in
age to the Glorieta) yielded helium and commercial amounts of natural gas at Model dome on
the Apishapa arch.
San Andres Limestone.—The San Andres Limestone is composed of dense, dark gray, earthy,
marine limestone that contains a few sandy layers. The San Andres is about 150 feet thick in
the southern part of the Las Vegas sub-basin, but
thins northward and wedges out a few miles
north of Las Vegas. The San Andres commonly is
2055
slightly fetid at outcrops and in the subsurface,
but has not yielded oil in the Raton basin.
Bernal Formation.—The Bernal Formation
consists of pink, orange, and red siltstone, shale,
fine- to coarse-grained sandstone, and some thin
beds of limestone and gypsum. The Bernal is
lithologically similar to the Yeso Formation. The
Bernal locally is as thick as 150 feet in the Las
Vegas sub-basin but is thinner at most places, and
is absent locally because of an erosion surface at
its top. The Bernal overlaps the San Andres Limestone and has been traced north of the Ocale
anticline. However, the Bernal is absent from the
outcrops at the eastern margin of the Sangre de
Cristos in the vicinity of the Cimarron arch. The
liernal is considered to be probably of Guadalupe n
age (Bachman, 1953), but the stratigraphy of the g
Bernal has not been studied carefully, and its age 32
is not substantiated yet by fossils. Possibly, some =»
of the rocks included in the Bernal are Triassic.
c3
-^—
Regional correlations.—At some outcrops on g
the eastern margin of the Sangre de Cristo uplift
north of Eagle Nest and in southernmost Colorado, the Sangre de Cristo Formation is overlain by
a poorly exposed sequence of orange, pink, and
red arkosic sandstone, siltstone, and shale containing a few thin beds of limestone and some
white sandstone (unnamed unit, Fig. 6). These
rocks are a maximum of 100-200 feet thick and
are similar to rocks cropping out from Purgatoire
River northward that were assigned to the Lykins(?) Formation of Permian(?) and Triassic(p)
age by Johnson and Baltz (1960, p. 1899-1902).
These rocks also can be identified in the subsurface of the northern Raton basin in both New
Mexico and Colorado. Part of the sequence in the
subsurface in southernmost Colorado has been
correlated with the Yeso Formation and Glorieta
Sandstone by Shaw (1956, p. 14-18), who postulates that the Yeso and Glorieta are present
throughout much of the Raton basin, but wedge
out westward in the subsurface just east of the
Sangre de Cristo Mountains. Shaw's correlation is
based on stratigraphic position and lithology;
however, the subsurface rocks he correlated with
the Yeso are similar also to parts of the Bernal
Formation, the unnamed unit, and the Lykins(?)
Formation (see Johnson and Baltz, 1960). The
pink and orange, fine- to coarse-grained sandstone
and shale correlated by Shaw with the Glorieta
*~
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25
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55
2056
ELMER H. BALTZ
SOUTH
NORTH
Southern Raton basin
(Las Vegas sub-basin)
CO
ID
o
2057
RATON AND SAN LUIS BASINS
Eagle Nest are^Mex. Colo.
(Cimarron
arch)
Northern Sangre de Cristo
Mtns.
©
tzs
uranetus
(9)
Graneros Shale
Ra|
stonCreek(7)Formotion
Entrada
Sandstone
Lykins(?)
Formation
Uohnson Gap Formation
Datum'- Top of Entrado Sontfsfont
jre de Cristo Formation
Fio. 6 -Diagram showing correUlio,
ian rocks and part of Mesozoic rocks.
Pre Cambrian
crystalline rocks
Scalt
(feet)
ELMER H. BALTZ
2058
tlo not resemble the gray, well-cemented, wellsorted Glorieta Sandstone of the Las Vegas subbasin, but they do resemble some of the exposed
rocks of the unnamed unit and the Lykins(P).
The unnamed unit and ils subsurface equivalents seem to correlate, at least partly, with the
Leonard and Guadalupe rocks that are 400-500
feet thick in the subsurface of the eastern limb
of the northern Raton basin and the Apishapa
arch (Shaw, 1Q56, p. 15; Norman, 1956; Oborne,
1<)56, p. 59-60). These rocks wedge out toward
the Wet Mountains and are not present at outcrops on the margins of this uplift.
Probably the Leonard and Guadalupe rocks
were deposited as a thin but widespread blanket
over most of the Raton basin region. These rocks
are mainly marine in the Las Vegas sub-basin, but
I heir possible equivalents, including the unnamed
unit and all or part of the LykinsC?) in the
western part of the northern Raton basin, seem
to be terrestrial. In the eastern part of the northern Raton basin, and on the Apishapa uplift and
eastern limb of the Sierra Grande uplift, the
Leonard and Guadalupe rocks seem to be marine.
The absence of these rocks from parts of the
Sierra Grande uplift (Wood et al., 1953), Cirnarron arch, and Wet Mountains-Apishapa arches is
mainly the result of Late Permian or Triassic
uplift and erosion, although it may be partly the
result of non-deposition.
KOCKS OF TKIASSIC AGE
A f t e r a long period of non-deposition and slight
erosion, terrestrial rocks of Late Triassic age
were laid down as a blanket of tluviatile sandstone and shale over much of the Raton basin
region. Triassic rocks are absent from the northwestern part of the Apishapa arch and the
Wet Mountains uplift, and are present only locally in the northern part of the northern Raton
basin.
Dockum Group.—In most of the Raton basin
region the rocks of Late Triassic age are referred
(o the Dockum Group. In the subsurface the
Dockum is 1.000-1,200 feet thick in the Las
Vegas sub-basin and 500-800 feet thick on the
Sierra Grande arch, generally being thinnest near
the crest of the arch. The Dockum is 300-400 feel
thick in the subsurface on the eastern limb of the
northern Raton basin, but thins northward and
westward toward the Apishapa arch and Wet
Mountains and the northern Sangre de Cristo
uplift (Oriel and Mudge, 1956, PI. 1), and finally
wedges out in the subsurface.
In the Las Vegas sub-basin and southern
Sangre de Cristo uplift the Dockum Group consists of the Santa Rosa Sandstone overlain by the
Chinle Formation (Fig. 6). The Santa Rosa
ranges in thickness from about 250-450 feet and
consists of thin to thick brown, gray, and reel
sandstone and inter-bedded thin to thick red shale.
The thickness changes because of the lenticularily
of the upper sandstone beds. At most places the
lower part is a massive unit of sandstone, as
much as 150 feet thick, that contains pebbles of
quartz, limestone, chert, and other sedimentary
rocks. Nodular limestone and pebbles of linn-stone and chert also are common at places in the
shale interbeds and some of the higher sandstones.
The thickness of the Chinle Formation ranges
from 600 to 900 feet in the Las Vegas sub-basin.
The Chinle consists mainly of red, purple, and
greenish shale but contains varied proportions of
interbedded red, brown, and gray sandstone, especially near the middle. Some of the shales are
calcareous, and thin limestone beds occur at
places. Lithologically, the sandstone and thin
shales of the middle member of the Chinle (Northrop and others, 1946) are similar to the Santa
Rosa, although the middle member is generally
thinner than the Santa Rosa, ranging from 30 (o
180 feet thick.
In the subsurface of much of the northern
Raton basin the Dockum Group consists of .\
basal unit of conglomeratic sandstone, 75-100 feet
thick, containing limestone and chert pebhley
that has been called the "unnamed unit" of the
Dockum Group by Oriel and Mudge (1956, p.
20-21). This unit probably correlates with the
Santa Rosa Sandstone, but the correlation ha*
not been established firmly. The unnamed unit b
overlain by red, purple, and green shale and interbedded sandstone and local thin cherty limestone, together as much as 275 feet thick, that
have been correlated with the Sloan Canyon Formation by Oriel and Mudge (19'56, p. 21). These
rocks probably are equivalent also to part of the
Chinle Formation.
Traces of asphaltic residues occur in \\ell
samples from the lower part of the Santa Ro-a
Sandstone at places in the Las Vegas sub-ba>in
RATON AND SAN LUIS BASINS
The source of this asphalt probably was the San
Andres Limestone. Some oil might have been introduced into the Santa Rosa from uplifted,
faulted, or eroded 1'aleozoic oil fields in the area of
the present Sangre de Cristo uplift on several occasions since Triassic time. However, the Santa
Rosa contains large amounts of "fresh" artesian
water and probably is mainly flushed now. Traces
of asphaltic residue occur also in the Triassic
rocks of the northern Raton basin. Although
some of the Triassic sandstones are moderately
porous and permeable, they are not favorably situated with respect to source beds in most of the
Raton basin to be considered as probable, large
petroleum reservoirs.
Johnson Gap Formation.—In the western part
of the northern Raton basin and the Sangre de
C'risto uplift from the Cimairon arch northward,
Triassic rocks range from a few feet to 700 feet
thick, with the thickness decreasing irregularly,
liut generally northward (Johnson and Baltz,
I960; Robinson and others, 1964, Fig. 86). The
Johnson Gap Formation (Fig. 6), which consists
of siliceous limestone conglomerate, gray and red
limestone, siltstone and shale, and gray and red
sandstone (Johnson and Baltz, 1960, p.
1897-1899), is 80-120 feet thick and may be
equivalent to part of the Santa Rosa Sandstone.
However, these rocks are similar also to the
middle and upper members of the Chinle Formation in the Las Vegas sub-basin, and the correlations are not established firmly. The Johnson Gap
Formation is equivalent (Johnson and Baltz,
1960) to part of the Dockum Group (Oriel and
Mudge, 1956, loc. 19, 20, PI. 1) in the subsurface
of the northern Raton basin, and on the Sierra
Grande and Apishapa arches. At least part of the
Lykinsf?) Formation of the northwestern part
of the Raton basin seems to be Triassic (Johnson
and Baltz, 1960, p. 1900-1901), but its relation to
the Triassic units has not been established.
Source areas.—The Upper Triassic sediments
of the Raton basin region were derived in part
from reworking of underlying Permian rocks.
Local monadnocks of Precambrian rocks supplied
some of the sediment, as indicated by coarse, angular quartzite fragments in the Dockum at
Temple dome on the Sierra Grande uplift in New
Mexico. However, Triassic deposits blanketed the
Raton basin region and the Sierra Grande and
Apishapa uplifts. A principal source of Triassic
2059
sediments must have been the San Luis uplift and
possibly Peimian rocks on its flanks. Probably
the ancestral Wet Mountains uplift also supplied
some of the detritus.
The presence of large amounts of detrital
chert, limestone conglomerate, and calcareous
shale in the Triassic rocks seems to indicate a limestone source terrane. In the southern part of
the Las Vegas sub-basin, the erosion of the underlying Bernal Formation and San Andres Limestone probably supplied the limestone pebbles of
the Santa Rosa Sandstone locally, but north of
this region another source is indicated. The only
obvious source of large amounts of limestone and
chert pebbles is the Magdalena Group of the
western parts of the Rowe-Mora and Central Colorado basins; thus, it is possible that these rocks
had begun to be deformed and uplifted slightly in
Triassic time.
The general northward thinning of the Triassic
seems to have been mainly the result of very
gentle warping and erosion in Jurassic time, although part of the thinning might be intraformational. The Dockum is folded into broad, low
(pre-Late Jurassic) anticlines which can be observed clearly at the southern end of the present
Ocate anticline, in the canyon of the Dry Cimarron River near the northeastern corner of New
Mexico, and at other places in the region.
KOCKS OF JURASSIC ACE
In Late Jurassic lime a widespread blanket of
shallow-marine and overlying terrestrial deposits
were laid down across the entire Raton basin region. The total thickness of these rocks ranges
from about 100 to 600 feet, the differences in
thickness being attributable mainly to an erosion
surface at the top of the Jurassic rocks.
Entrada Sandstone.—The basal Upper Jurassic
unit in almost the entire region is the Entrada
Sandstone (Fig. 6). This sandstone has been
called the Exeter, Wingate, or Ocate Sandstone in
various reports, but is now (McLaughlin, 1954, p.
88-91; Johnson, 1959, p. 95) generally correlated
with the Entrada Sandstone of Utah. The Entrada ranges in thickness from 20 feet to 120 feet
with considerable local variation. In Colorado the
thickness varies, but the Entrada thins generally northward toward the Wet Mountains, and is
absent from the eastern flank of the uplift.
The Entrada is a white to pink and red, fine- to
2060
ELMER H. BALTZ
coarse-grained, moderately well-sorted sandstone.
Most of the sand grains are rounded and frosted
quartz, but grains of red and green chert and
weathered feldspar also are present. The cement
generally is calcareous and, locally, slightly gypsiferous.
An eolian origin of the Entrada has been postulated because of the sweeping tangential crossbeds that are common at many places. However,
much of the bedding is parallel and even, and the
Entrada intertongues with overlying deposits of
limestone, fine elastics, and evaporites. It seems
likely that the Entrada was deposited on and near
beaches and in near-shore marine environments
during the transgression of a shallow sea.
The Entrada lies unconformably on Triassic
rocks in the subsurface of most of the region, but
overlaps the Triassic in the northern Raton basin
and Apishapa arch and rests on the Sangre de
Cristo Formation in the subsurface and at outcrops in the northern Sangre de Cristo uplift and
Wet Mountains uplift. At Williams Creek on the
southwestern side of the Wet Mountains (loc. 12,
Fig. 6) the Entrada is arkosic, and it seems to
have been derived from a nearby Precambrian
terrane. However, the contact of the Entrada and
the Precambrian is faulted (Johnson, 1959, PI.
4). The Entrada laps onto Precambrian rocks in
the present Brazos uplift in New Mexico and in
the San Juan Mountains and Gunnison uplifts in
Colorado, indicating that the ancient San Luis
uplift was a positive area at the time of deposition of the Entrada. At places in the Las Vegas
sub-basin and on the Sierra Grande uplift the Entrada rests on red and white sandstones which
have been correlated tentatively with the Glen
Canyon Group of Late Triassic and Jurassic age.
The stratigraphy and correlations of these rocks
are not known well. Rocks near Mora River
south of Ocate anticline that are similar to the
Naranjo Formation of Bachman (1953) consist
of reworked red Chinle sediments that grade
southward into the lower part of the Entrada.
Similar relations between the Sheep 1'en Sandstone of Parker (1933) and the Entrada occur
along the flanks of pre-Entrada anticlines in the
canyon of the Dry Cimarron River near the northeastern corner of New Mexico. Locally, the
Entrada wedges out across these anticlines. These
relations seem to indicate slight folding, reworking, and sorting of Triassic sediments on some
anticlines during deposition of the Entrada.
Toilitto Limestone and Ralston Creekf?) Furmation.—The Entrada Sandstone is overlain by
and intertongues with a unit of evenly bedded,
probably mainly marine, rocks that consists i>f
varied facies of limestone, green and red shale,
gypsum, and thin sandstone (the "middle unit of
Jurassic age" of Oriel and Mudge, 1956). These
rocks are present throughout the Raton basin region where they range in thickness from 50 tu
100 feet. In the southern Sangre de Cristo uplifi
west of Las Vegas the unit consists mainly of
gray, finely laminated, fetid limestone correlated
with the Todilto Limestone of western New Mt.\ico (Northrop and others, 19-46; Baltz and Hathman, 1956). The Todilto tongues out northward
and eastward into a sequence of locally gypsiferous, reddish to waxy-green shale that contains
interbedded thin, fine- to medium-grained sandstone, and red chalcedony beds. This sequence wa>
correlated with the Wanakah Formation of southwestern Colorado (Hachman, 1953; Wood el d,
1953; Johnson and Stephens, 1954). Johnson
(1962, p. C40-C54) assigned these rocks in the
Colorado portion of the Raton basin to the Ralston Creek(?) Formation. They are generall)
equivalent to the Ralston Formation of Freclerickson et al. (1956) at the eastern edge of ihe
Front Range and the Canon City embaymenl in
Colorado.
Morrison Formation.—The Ralston Crceki'-i
Formation is overlain by Huviatile deposits of Ihc
Morrison Formation throughout the Raton ba.-in
region. The thickness of the Morrison ranges frnm
about 150 to 400 feet, with considerable local
variation because of regional warping, local genlle
folding, and erosion of upper beds prior to deposition of the overlying Purgatoire Formation of
Early Cretaceous age. The Morrison generally is
thickest in the western parts of the Raton basin,
and thins irregularly eastward onto the Sierra
Grande and Apishapa arches and the Wet Mountains uplift.
The Morrison consists of varied proportions of
red, gray, and brown sandstone and conglomeraie.
and interbedded red, gray, and green shale and
thin local limestone beds. The regional stratigraphy of the Morrison in the Raton basin has noi
been studied in detail, and little is known of the
distribution of units of less-than-formational rank
The greenish to reddish mudstone and shale and
interbedded coarse-grained and conglomeratic
sandstone of the upper part of the Morrison arc
RATON AND SAN LUIS BASINS
2061
Members of the Purgatoire in the Front Range
of Colorado (Waage, 1953). Recently, T. G.
McLaughlin (U.S. Geol. Survey Water-Supply
Paper 1805, in preparation) has designated the
lower unit the Cheyenne Sandstone Member, and
the upper unit the Kiowa Shale Member of the
Purgatoire Formation in the subsurface of the
Apishapa arch. Rocks equivalent to the Cheyenne
differ considerably in thickness, but are generally
100-150 feet thick in the northern Raton basin,
and rocks tentatively correlated with the Cheyenne are 50-140 feet thick in the Las Vegas subbasin. Rocks equivalent to the Kiowa in the
northern Raton basin are 15-45 feet thick, and
the shaly rocks tentatively correlated with the
Kiowa in the Las Vegas sub-basin generally are
only 20-40 feet thick, and locally are absent from
the western edge of the basin.
The Kiowa contains marine fossils in southeastern Colorado and probably is mainly a shallowwater marine deposit throughout most of its extent, although it may have accumulated in lagoons or swamps at the west. At places along the
western margin of the Raton basin the Purgatoire
and the overlying Dakota Sandstone can not be
differentiated with assurance, and they have been
mapped together as the Dakota Sandstone by
some authors. The Cheyenne Sandstone Member
is porous and permeable and generally yields
large amounts of water in wells. At a few places
in the northern part of the basin the Cheyenne
has produced "shows" of oil, but these were
flooded out by water.
Dakota Sandstone.—The Purgatoire Formation
is overlain throughout the Raton basin and the
KOCKS OF CRETACEOUS AGE
In Early Cretaceous time the Raton basin re- arches at the east by gray to buff sandstone and
fion and the ancient positive areas became parts interbedded gray shale of the Dakota Sandstone
of the extensive Rocky Mountain geosyncline. of Early Cretaceous age. In New Mexico the DaMore than 3,500 feet of sediments, largely ma- kota commonly is only 30-60 feet thick. In Colorine, accumulated in the Raton basin region be- rado the Dakota thickens northward to 100-150
feet. At the southeastern side of the Wet Mounfore the end of Cretaceous time.
Purgatoire Formation.—The Purgatoire For- tains the Dakota and Purgatoire together are as
mation of Early Cretaceous age rests unconform- much as 650 feet thick and are said to be a delihly on the Morrison Formation and is present taic deposit there (Waage, 1953, p. 19-20). In the
11 most of the Raton basin and on the Sierra subsurface of much of the northern Raton basin
' Grande and Apishapa arches. Throughout much the Dakota is about 100 feet thick. In general,
of this region the Purgatoire consists of a lower the Dakota seems to thicken slightly from east to
tonglomeratic sandstone member and an upper west.
At places, especially in the outcrop areas at the
member composed of varied proportions of gray
western
margin of the Raton basin, the Dakota is
carbonaceous to coaly shale and interbedded thin
sandstone. These members generally are equiva- nearly all sandstone and contains lenses of conlent to the Lytle Sandstone and Glencairn Shale glomerate. However, at most places the Dakota
jmilar to the Brushy Basin Member of the Morison of the Colorado Plateau. Some of the san:iSone and conglomerate in the upper part of the
\Inrrison is similar to the overlying Purgatoire
"ormation, causing local confusion in determining
:he top of the Morrison.
Source areas and petroleum possibilities.—Part
if the sediments of the Entrada in the Raton
:asin are reworked Triassic sediments. However,
niuth of the sediment of the Entrada, Ralston
t"rcek(?), and part of the Morrison was derived
j'rum the central New Mexico highland south of
the Raton basin, as shown by facies changes and
..iulhward thickening of sandstone units in eastientral and west-central New Mexico. Some of the
aliment probably was derived also from sources
in Oklahoma and Kansas. The chert-pebble conilcimcrate of the upper part of the Morrison may
have been derived from the west, and the ancient
San Luis and Wet Mountains uplifts must have
contributed some of the elastics.
Although some of the Jurassic rocks, especially
the Entrada Sandstone, are porous and permeable, they are not generally in favorable stratigraphic positions with respect to possible source
beds to be likely petroleum reservoirs and have
not yielded oil or gas where they have been
itsted in the Raton basin. The thin Todilto Limeslone in the southern part of the Las Vegas subbasin is fetid, and trace oil stains in the Entrada
can be attributed to it. Dead oil stains occur in
the Entrada and Ralston Creek(?) at Tercio anlicline in the northern Raton basin.
2062
ELMER II. BALTZ
consists of several thin to thick, even-bedded
sandstones that are separated by thin gray shales.
Some of the sandstones are fine-drained to finely
conglomeratic, whereas other beds consist of
clean, well-sorted, loosely cemented sandstone. In
general, the sandstone beds thin slightly eastward
and the proportion of shale increases slightly
eastward.
Much of the Dakota is marine, but in the
western part of the basin it contains stream-channel sandstones and at places may be mainly terrestrial. The upper part of the Dakota grades
into the marine rocks of the overlying Graneros
Shale. "Shows" and stains of oil have been found
in the Dakota at a few places in the Las Vegas
sub-basin and at many places where it has been
tested in the northern Raton basin.
Graneros Shale, Greenhorn Limestone, and
Carlile Shale.—The Graneros Shale, Greenhorn
Limestone, and Carlile Shale are marine rocks
that are present throughout a large region of the
Great Plains including the Raton basin and its
bounding arches at the east. The Early Cretaceous-Late Cretaceous time boundary is within
the Graneros Shale.
The Graneros rests conformably on the Dakota
Sandstone and consists of dark gray shale that
contains thin beds of bentonite, a few thin beds
of limestone, and locally a minor amount of finegrained sandstone. The Graneros is 185-380 feet
thick in the northern Raton basin, and is 215-250
feet thick in the Las Vegas sub-basin. The Greenhorn Limestone rests conformably on the Graneros, is 30-80 feet thick in the northern Raton
basin, and is 20-60 feet thick in the Las Vegas
sub-basin. The Greenhorn is composed of thin
beds of limestone and interbedded calcareous to
chalky shale. The Carlile Shale rests conformably
on the Greenhorn, is 165-235 feet thick in the
northern Raton basin, and is 220-340 feet thick in
the Las Vegas sub-basin. The Carlile is a dark
gray shale that contains thin limestone beds, septarian concretions, and, in the upper part, sandy
shale and thin calcareous sandstone beds. Where
the upper calcareous sandstones form a distinct
unit and are fairly thick (15-25 feet), they are
called the Codell Sandstone Member of the Carlile. "Shows" of oil and gas have been reported
from the Graneros and Carlile in the northern
Raton basin.
Niobrara Formation.—The Niobrara Formation lies on the Carlile Shale throughout most of
RATON AND SAN LUIS BASINS
the Raton basin and on the Apishapa and Sic:| :he overlying Trinidad Sandstone. "Shows" of oil
Grande arches. The Niobrara is about SCO ftt 1 iml gas have been encountered in fractured
I hick at outcrops on the flanks of the Wet Muu 'icrre Shale in the northern Raton basin.
tains (Johnson and Stephens, 1954), and i- « Trinidad Sandstone and Vermejo Formation.—
much as 630 feet thick in the subsurface of it. The Trinidad Sandstone and the overlying Vernorthern Raton basin. In the southern part o( il.- m-jo Formation are present in the northern
Las Vegas sub-basin (he Niubrara is absent U Rjion basin in the roughly triangular region because of Quaternary erosion, but as much a* « < i»ccn Ute Park, a point about 13 miles east of
feet of rocks probably equivalent to the Niolirj: Katon, New Mexico, and the southern part of
are preserved in the trough of the basin a d Greenhorn anticline in Colorado. A few miles
jutheast of Huerfano Park, the Poison Canyon
miles northwest of Las Vegas.
The Niobrara Formation is marine. The l»ut Formation of Paleocene age truncates the Trinipart of the formation consists of thin liim-Mon iij and Vermejo and rests unconformably on
and interbedded shale, the Fort Hays Limr.-tH.: ihc Pierre Shale in the north (Johnson et al.,
Member, that ranges in thickness from 25-55 fn I')5S). The Trinidad and Vermejo are absent
in the northern Raton basin (Cobban, 1956. | liom the westernmost part of the basin in New
26) to 10-20 feet in the Las Vegas sub-basin. Ti« Mexico between Ute Park and a point west of
upper part, the Smoky Hill Marl Member, mi: Vermejo Park anticline, also because of angular
sists of marly shale with interbedded thin lin.c unconformity with the Poison Canyon Formation
stone and sandy shale. Locally the middle pun i, % 7).
the Smoky Hill contains distinct beds of fairn The Trinidad Sandstone is 0-300 feet thick. It
clean sandstone that are as much as 10-30 fit h thickest near the axis of the northern Raton
thick. "Shows" of oil and gas have been repoiin basin where it ranges from 140 feet thick at the
from fractured Niobrara Shale in the norllu;: siuth to about 300 feet thick northward from
i'urgatoire River (Johnson and Wood, 1956, Fig.
Raton basin.
Pierre Shale.—The Pierre Shale lies on (fct I and p. 712). Along the western margin of the
the Trinidad is 80-220 feet thick and, on
Niobrara Formation in much of the Raton basin
but has been eroded from parts of the eaili-rn [he eastern limb of the basin, 80-100 feet thick
Hanks of the basin and from the southern part <>: Johnson and Wood). The Trinidad consists of
the Las Vegas sub-basin. In the trough of ihr Jightly arkosic, fine- to medium-grained sandnorthern Raton basin southeast of Huerfano Paik Hone with some interbedded thin shale. These sedthe Pierre is as much as 2,300 feet thick (John iments were deposited in beach and near-shore
son and Wood, 1956, p. 710). At wells near ihr sivironments during the closing phases of marine
Colorado-New Mexico border the Pierre is alxm! ^position. The Trinidad intertongues with the
2.100 feel thick, and near the southern margin <>i iverlying Vermejo Formation (Johnson and
the northern Raton basin the Pierre is aUiui ( Vuod) and with the underlying Pierre Shale
1,600 feet thick (Johnson and Wood). South u: (Harbour and Dixon, 1956).
here much of the Pierre has been removed \>\ Excellent "shows" of oil have been reported
Quaternary erosion and only the lower part is torn wells that penetrate the Trinidad in Colorad>, and asphaltic residues and oil seeps occur in
preserved.
The Pierre is marine and consists mainly of de Trinidad in the Cimarron River canyon in
dark gray non-calcareous shale, but contains i Sew Mexico, and also on Alamo dome (Johnson
few thin beds of limestone, sandy shale, and 'nd Stephens, 1954; Creely and Saterdal, 1956b)
sandstone. A zone about 100 feet thick that con- it Colorado. The Trinidad is an attractive drilling
sists of the Apache Creek Sandstone Member «kjective in the northern Raton basin because it
(Scott and Cobban, 1963, p. 1399) and other beds ra the shallowest of the Cretaceous marine sandof calcareous sandstone and siltstone ociurs stones in much of the region.
about 500 feet above the base of the Pierre at The Vermejo Formation thickens westward
outcrops and in the subsurface of the northern (mm a wedge near Raton to about 550 feet
Raton basin. The upper 200-300 feet of the ii the trough of the northern Raton basin near
Pierre consist of interbedded shale and thin 'tie Spanish Peaks in Colorado (Johnson and
sandstone that grade into and intertongue w i l h 'Wood, 1956, Fig. 5). The Vermejo thins west-
2063
ward from the trough and averages about 250
feet in thickness along the western margin of the
basin (Johnson and Wood). The Vermejo Formation is composed of varied proportions of buff to
gray shale, carbonaceous shale, coal, and slightly
arkosic fine- to medium-grained sandstone that
were deposited in swamps and on Hood-plains
near the coast of the eastward-retreating Cretaceous sea.
Source areas.—Before Cenozoic orogeny and
erosion, the Cretaceous rocks probably formed a
thick blanket across the entire Raton basin region, the ancient positive areas on the east, and
most of the region on the west. However, regional variations in thickness and lilhology indicate that this blanket was not uniform, and that
the ancient tectonic elements influenced sedimentation to some degree.
Part of the Purgatoire Formation consists of
reworked sediments of the underlying Morrison,
but part probably was derived from the Precambrian of the Wet Mountains uplift, as shown by
onlap near the southeastern edge of that uplift
(R. B. Johnson, oral communication, 1965) and
by the deltaic sediments of the Purgatoire and
Dakota in that area (Waage, 1953). The Dakota
Sandstone in the present Brazos uplift in New
Mexico contains coarse Precambrian detritus, and
laps onto the Precambrian at places, indicating
that the ancient San Luis uplift supplied at least
some of the Early Cretaceous sediment.
During most of Late Cretaceous time the
thick, shaly sediments that accumulated in the
Raton basin region probably were derived mainly
from orogenic areas in southwestern New Mexico, Arizona, and central Utah that supplied the
detritus of the Mesaverde Group and related
rocks. However, the differences of thickness of
the various shale units indicate that the northern
Raton basin, the Cimarron arch, and the Las
Vegas sub-basin underwent slightly different
amounts of subsidence. Possibly, the thin but
widespread sandy units such as the Codell Sandstone Member of the Carlile Shale, the sandy beds
of the Smoky Hill Marl Member of the Niobrara, and the Apache Creek Sandstone Member
of the Pierre were derived from areas far at the
west. On the other hand, it is possible also that
some of this sand might have been derived from
island areas on the San Luis uplift. Such sources
might be indicated by the northeastward thinning
of the Mancos Shale of Late Cretaceous age in
2064
ELMKR H. BALTZ
RATON AND SAN I.U1S HAS1NS
H
§
fc
n. o c .
Ihe Sun Juan basin west of the ancient uplift, anil
hy unconformities within the Mancos of the eastern San Juan basin that were reported by Dane
( I 9 6 0 ) . Similar unconformities might exist between some of Ihe shale units in the Raton basin,
Iml these rocks have not been studied in the delailed manner necessary to determine the relationships.
The thin sandstone beds in the upper part of
the I'ierre Shale are the first direct evidence of
l.aramide orogeny in the Raton basin region
(Johnson and Wood, 1956, p. 7 1 2 ) . The interlunguing relations of the I'ierre, Trinidad, and
Vermejo Formations (Fig. 7) indicate that the
Cretaceous sea retreated eastward or northeastward across the Raton basin region, and that sediments were derived from the west. Parts of the
I'ictured Cliffs Sandstone and the Fiuitland Formation (homogenetic equivalents of the Trinidad
and Vermejo), both of Late Cretaceous age in
the San Juan basin, were derived from the east
ur northeast (Halt/., in preparation). This indicates that at least the southern part of the an•.ictit San Luis uplift was risinr in late Montana
time and was a source of sediments supplied to
the Cretaceous sea in both regions.
KOCKS OF LATEST CKETACKOUS A N D
T K K T I A R Y Af.ES
The major orogenic events that produced Ihe
present Raton basin and its bounding uplifts
began in latest Cretaceous time and continued episodically through Oligocene time. The terrestrial
rocks that record the stages of orogeny are pre>erved (inly in the northern Raton basin and Huerfano I'ark. Most of Ihe Tertiary history of Ihe
l.as Vegas sub-basin and the Sierra Grande and
Apishapa arches can be inferred only by analogy
will] events in the northern part of the basin.
The details of the latest Cretacecus and Tertiary
stratigraphy and history are discussed hy Johnson
and Wood (1956) and Johnson (1959). The frllowing discussion is summarized largely from
these papers.
Raton Formation and Poison Canyon Formation.—The Raton Formation of Late Cretaceous
and Paleocene age lies on the Vermejo Formation
and consists of fine- to coarse-grained arkosic
sandstone, gray shale, and numerous beds of coal.
At most places Ihe basal part of Ihe Raton is a
pebble-bearing conglomerate. The Raton Formation is a swamp and Hood-plain facies, as much as
20o 5
1,700 feet thick in the trough of the basin, that
grades westward into and intertongues with a piedmont facies of the lower part of the overlying
Poison Canyon Formation of Paleocene age (Fig.
/'). This lower part of the Poison Canyon consists of coarse, arkosic sandstone, conglomerate,
and t h i n yellow shale which were derived mainly
from Precambrian tenanes on Ihe west. The Poison Canyon is as much as 2,500 feet thick in the
trough of Ihe basin. The angular unconformity
between the Poison Canyon and the Cretaceous
rocks in the western part of the basin (Fig. 7)
shows t h a t by Paleocene lime the Sangre de Crislo uplift had begun to form in the western parts
of the ancient Rowe-Mora and Central Colorado
geosynclines. The ancient San Luis uplift was elevated, as shown by the facies of Paleocene rocks
in the San Juan ba^in ( I t , i l l / , in preparation),
and was a hinterland west of the crumpled and
rising troughs of the ancient geosynclines. The
Raton anil the Poison Canyon are conformable in
much of the basin, but on the eastern and western margins of Huerfano Park the Poison Canyon
truncates and overlaps the Raton, Vermejo, and
Trinidad, and locally truncates the Pierre Shale
lo rest on the Niobrara Formation. Coarse conglomerates of Ihe northern part of the Poison
Canyon must have been derived mainly from the
rising Sangre de Cristo u p l i f t , bill part of the formation probably was derived from the newly rising Wet Mountains uplift.
''Shows" of oil and gas were found in the Poison Canyon Formation at Alamo dome (Crcely
and Saterdal, l')Sdb, p. 71) in the vicinity of the
overlap of the Trinidad Sandstone.
Citcharti Formation.—The Cuchara Formation
of early Eocene age consists of varicolored conglomeratic sandstone and inlerbedded variegated
shale. The Cuchara rests unconformably on the
Poison Canyon, overlaps it, and extends into the
northern part of Huerfano Park where it rests on
the Pierre Shale. The Cuchara locally is absent
from the eastern part of Huerfano Park, but is at
least 5,000 feet thick in the trough of the basin
near the Spanish Peaks. The sediments of the
Cuchara probably were derived from rocks ranging from Precambrian through Paleocene. The
red sediments of the Cuchara probably were derived mainly from redbeds of the Sangre de Crislo formation in the strongly uplifted region west
of Ihe basin, and also from the Wet Mountains.
Huerfano Formation.—After deposition of the
2066
ELMER H. BALTZ
Cuchara, another episode of uplift occurred in tains area. The Devils Hole overlaps the overthe regions west and north of the Raton basin. thrust plates in the western part of Huerfanu
During and a f t e r this orogenic episode the Huer- Park. These relations provide evidence of the prc-fano Formation of Eocene age was deposited un- Miocenel?) age of (he major episode of thrustconformably on the Cuchara Formation. The Huer- ing in the Sangre de Cristo uplift. The Wt-l
fano is composed of variegated shale and inler- Mountains fault cuts the Devils Hole at the eastbedded conglomeratic sandstone. An outlier of ern edge of Huerfano Park and indicates sonic
the Huerfano Formation occurs in the western u p l i f t of the U'et Mountains, or depression of thepart of the Spanish Teaks, but most of the for- Huerfano Park segment of the Raton basin since
mation is in Huerfano Park where it is as much middle Tertiary time.
as 2,000 feet thick, and where it rests with anguSEDIMENTS AND ROCKS OF LATE TERTIARY
lar unconformity on rocks as old as the Pierre
AND Q U A T E R N A R Y AC.ES
Shale.
In latest Eocene or in Oligocene time the presThe late Tertiary and Quaternary history nf
ent Raton basin and its bounding uplifts were the Raton basin has not been studied in detail
delineated in essentially their present structural However, it appears that much of the region, informs because of strong thrusting and uplift of cluding the Sangre de Cristo uplift, was reduced
t h e Sangre de Cristo region and downwarp of the by erosion to an eastward-sloping compound surbasin. The western part of the Sangre de Cristo face of low relief prior to deposition of the Ogaluplift probably still merged with the ancient San lala Formation of Pliocene age. The Ogallala is
Luis uplift prior to the late Miocene and Pliocene preserved mainly east of the crests of the Sierra
formation of the Rio Grande trough. Sills, dikes, Cirande and Apishapa arches.
and stocks of intermediate to silicic composition
Epeirogenic uplift of the entire region occurred
were intruded at places along the western margin in late Tertiary time, at the time the Rio Grande
of the northern Raton basin and in the area of trough was being formed. Andesitic and basaltic
the present Spanish Peaks in latest Eocene or Ol- dikes, plugs, and volcanic Hows of late Tertiary
igocene time. The laccolithic intrusions at Turkey and Quaternary age in many parts of the Raton
Mountain dome and in the Temple dome-Capulin basin are associated with this period of regional
anticline area of the Sierra Grande arch also may deformation and large-scale erosion. Extensivebe of early Tertiary age.
basaltic Mows of probable late Tertiary age cap
Parisita Conglomerate.—After the final major high mesas that extend eastward for almost 100
I.aramide orogenic episode the pebbles, cobbles, miles from Raton along the Colorado-New Mexiand boulders of the Farisita Conglomerate of Oli- co line, liasalt flows were extruded from centers
gocene(?) age were deposited on eroded rocks near the axis of the Sierra Grande arch in New
ranging in age from Eocene to Precambrian. The Mexico, along the western margin of the basin
Farisita is preserved only in Huerfano Park south of the Cimarron arch, and in the cenlral
where it is as much as 1,200 feet thick. Probably and northeastern parts of the Las Vegas sulimost of the sediments of the Farisita were de- basin.
rived from the west, but the Farisita laps onto
Oil was found in fractures in a thick igneous
Precambrian rocks at (he western margin of the sill at Ojo anticline (Creely and Saterdal, 195fia.
\Vet Mountains uplift which probably also was a p. 68-70) in (he northern part of the Raton basin,
source of the sediments of the Farisita.
indicating lhat the petroleum possibilities of areaDevils Hole Formation.—The Devils Hole For- of igneous intrusion should not be discounu-d
mation of M i o c e n e f ? ) age rests unconformably merely because of the presence of igneous rocks.
on the Karisila Conglomerate. The Devils Hole is
CONCLUSIONS
preserved only in the Huerfano Park area and is
25-1,300 feet thick. The formation consists of a
The study of the stratigraphy of the Rulcm
western fades of red conglomeratic sandstone de- basin indicates that this region has been a basin.il
rived from (he Sangre de Crislo u p l i f t , and an area for mosl of its history since Early Penii>yleastern fades of waler-laid luff and volcanic con- Viiiiian lime. The thick marine geosynclinal >nliglomerate t h a i contains fragments of Precam- ments of Ihe Magdalena Group, especially thebrian rucks and was derived from the U'et Moun- gray and black .shale, seem to be likely sources uf
RATON A N D SAN LUIS HASIXS
hydrocarbons. The shelf facies of the Magdalena
in the southern part of the Las Vegas sub-basin,
and Ihe elastics of the M i n t u r n Formation in the
H u e r f a n o Park region, are potential reservoir
rocks which were formed at the time when connate lluids were being expelled from the geosynclinal facies because of compaction. The depression of the Rowe-Mora and Central Colorado basins relative to the Wet Mountains, Apishapa,
and Sierra Grande uplifts and the Cimarron arch
in Late Pennsylvanian and Early Permian time
may have resulted in the formation of combination stratigraphic-struclural traps because of
updip truncation of the Magdalena Group by the
Sangre de Cristo Formation. This event occurred
also during the time when connate fluids probably
were being expelled from the geosynclinal areas.
The subsequent history of the region indicates
that the Paleozoic basinal areas of the presentday Raton basin remained intact or were accentuated during later tectonic events. Therefore, it is
probable that traps in Ihe areas of truncation of
(he Magdalena Group may have remained more
or less intact.
Although Permian, Triassic, and Jurassic rocks
contain porous, permeable sandstones that might
he suitable reservoirs, these rocks are not generally in favorable positions with respect to possible source rocks to be considered as likely
sources of petroleum. It is possible that in someplaces faulting may have placed these rocks in
favorable positions for influx of petroliferous
fluids, especially along the western margin of the
Raton basin.
The Cretaceous rocks are the most attractive
objectives for oil and gas exploration in much of
the Raton basin, especially the northern part, because of their widespread extent, relatively shallow depth, and lithologic types. The thick shales
are likely sources of hydrocarbons, and some of
Ihe confined sandstones are suitable reservoir
rocks. The relatively thin and shallow Cretaceous
sequence in the Las Vegas sub-basin is less attractive because it probably is mainly flushed, although "shows" of gas have been reported from
the Greenhorn and Carlile interval and traces of
oil have been found in the Dakota.
Nearly all the major anticlines in the Raton
basin that involve Cretaceous rocks have been
partly tested by drilling. No really commercial
accumulations of hydrocarbons have been found
yet in the Cretaceous rocks, although a few wells
2067
in Ihe northern part of the basin produced small
amounts of oil or gas at the Ojo, Escondido, and
Garcia anticlines. However, encouraging multiple
"shows" have been found not only in sandstone
but also in fractured shale on some of the structures in the northern part of the basin. Overthrust structures along the western margin of the
basin (Johnson ft al., 1058; Johnson. l l >5») offer
mainly untested possibilities of both fault traps
and anticlinal accumulations in Ihe Purgatoire
and Dakota, and of fractured-shale reservoirs as
well. The overlaps of the Trinidad and Vermejo
and part of the Pierre by the Poison Canyon and
higher Tertiary rocks offer possibilities of stratigraphic-structural traps south of Huerfano Park.
Hydrodynamic traps also might occur in the Cretaceous sandstone u n i t s on monoclinal folds or
anticlinal bends on both Ihe eastern and western
limbs of the Raton basin.
Several kinds of slratigraphic traps probably
exist in the Cretaceous rocks, especially on the
eastern limb of the basin. The slight eastward
thinning of the Dakota seems to be accompanied
by a general eastward diminution in grain size,
and local strand-line or bar accumulations of
clean, well-sorted sandstone might be present. If
the differences in thickness of the Graneros, Carlile, Niobrara, and Pierre Shales in the Las Vegas
sub-basin, the Cimarron arch, and the northern
Raton basin are the results of local or regional
unconformities, offshore bar accumulations of
winnowed, clean shoestring sandstones might be
present. Outcrop data indicate lhat tongues of the
Trinidad Sandstone wedge out eastward into the
Pierre Shale, and such updip wedge-outs also
must be present in the subsurface of the eastern
limb of the northern Raton basin. Not enough is
known of the details of Cretaceous stratigraphy
in the Raton basin to evaluate the probability of
occurrence or the locations of any of these kinds
of stratigraphic traps, but what is known about
the regional stratigraphy indicates that such traps
are possible.
NOTES ON SAN Luis BASIN
G E N E R A L TECTONIC DESCRIPTION
The San Luis basin in south-central Colorado
and north-central New Mexico is an intermontane
s t r u c t u r a l depression between the San Juan
Mountains volcanic field and Bra/os uplift at the
west and Ihe Sangre de Cristo uplift at the east
(Fig. 8). This s t r u c t u r a l basin includes the phys-
RATON AND SAN LUIS HASINS
ELMER H. BALTZ
2069
adjacent to the basin for most of its length. A cene and possibly Oligocene age. Generally equivScanty well data indicate that Ihe volcanic rocks
major fault zone, downthrown on the west, ex- alent rocks lying on the Blanco Basin in the
raphic fealure in Colorado that was described of the San Juan Mountains (Potosi Volcaniclends north from the western spur of the Sangre northern part of the Brazos uplift and in the San
t h e San Luis Valley by Siebtiithal (1910, p. Group) dip east beneath Miocene and Pliocene
de Cristos in New Mexico, into the basin along Juan Mountains in Colorado are the Potosi Vol. who indicated (hat the valley also extends sediments and lie more than 5,000 feet below the
ihe western side of San Pedro Mesa, to a point canic Group of middle and late Tertiary age and
uthward about IS miles into New Mexico (see surface northwest of Alamosa, whereas these volnorth of San Luis, Colorado (U.S. Geol. Survey, the overlying Los Pinos Gravel of Miocene and
ip of physiographic divisions on Fig. 8). Upson canic rocks crop out and form parts of the San
1935). The Culebra Reentrant is a graben Pliocenet?) age |Larsen and Cross, 105(>, p.
').?')) extended the term San Luis Valley to in- Luis Hills in the vicinity of the Rio Grande south
18o). The Los I'inos Gravel and Ihe Carson Coni Upson, 1939, p. 734).
ide areas farther south in New Mexico. Upson and southeast of Alamosa (U.S. Geol. Survey,
glomerate are mainly older than Ihe Santa Fe
In
most
of
the
San
Luis
basin
south
of
Alamo'>39, p. 722 and Fig. 2) named and described
Group, but their upper parts may be contempora1935). This may indicate that the Alamosa seg-a, the surface rocks are volcanic. The youngest
e. Alamosa Basin, San Luis Hills, Taos Plateau, ment of the basin is bounded, north of the San
neous with the sediments of part of Ihe Santa Fe.
,,f
these
rocks
are
the
thick
basalt
flows
that
cap
ustilla Plains, and Culebra Reentrant as physio- Luis Hills, by concealed northeast-trending faults
In the Brazos u p l i f t the volcanic rocks overlap
the Taos Plateau west of the Rio Grande and
aphic subdivisions of the valley. The structural
the thin early Tertiary sedimentary rocks and
that are downthrown toward the northwest
,,.cur
at
places
east
of
the
river.
These
basalts
in Luis basin embraces all of these physiograph(Upson, 1939, p. 7 2 7 - 7 2 8 ) .
have been tilted east slightly and are overlain, in rest on Precambrian crystalline rocks. Larsen and
subdivisions, and its southern boundary has
The Alamosa segment is a topographically,
ihe Costilla Plains east of the Rio Grande, by Cross (195o, PI. 1't indicate that Ihe Polosi volcen defined (Kelley, 1956, p. 109) as the Embu- nearly tlat interior drainage basin whose deepest
Quaternary alluvial deposits, derived from the canics rest on Precambrian granite at small out(i constriction southwest of Taos.
part is northeast and east of Alamosa where seveast, that mainly mask the faulted eastern crops in T. ,33 N., Rs. 5 and 0 E., in the canyon
The San Luis basin is about 135 miles long and eral lakes and playas are present. In this area
of the Conejos River.
boundary of the basin.
, almost 55 miles wide north of San Luis, Colo- sediments of Pliocene or Pleistocene age arc
A similar sequence of conglomeratic redbeds
Very
little
is
known
about
the
subsurface
straado. The San Luis basin is the northernmost of more than 2,000 feet thick (Powell, 1958, p.
and overlying tuffaceous conglomerate that was
ligraphy
of
the
San
Luis
basin.
Most
of
the
basin
i series of linked, echelon, tilted blocks and com- 22-24), but these sediments thin toward the west
named Ihe Piiuris Tuff by Cabot (1938) crops
is filled by sediments and basaltic to andesilic
ilcx grabens that are called, collectively, the Rio and southwest, indicating that p a r t ' o f the t i l l i n g
out in the Picuris Mountains near the eastern
volcanics
of
the
Santa
Fe
Group
of
Miocene
to
Irande trough or depression. The Rio Grande and depression of the basin occurred as late as
l'leistocene(?) age that were deposited during margin of Ihe San Luis basin south of Taos, and
rough extends southward about 450 miles from Pleistocene time. This part of the basin may have
ihe downfaulting of the basin. Outcrops in the is preserved locally in the western part of the
-outh-central Colorado entirely across New Mexi- subsided 12,000-15,000 feet, relative to the
pounding uplifts and at places on the margins of Sangre de Cristo uplift in the area south of Taos
co. This trough was formed in middle and late Sangre de Crislo u p l i f t , since middle Tertiary
(Montgomery, 1953) and between Taos and
,he
basin indicate that the Santa Fe Group is un1'ertiary time, and structural adjustments continEagle Nest. The Picuris was estimated to be as
time.
ilerlain at many places by volcanic rocks and conued to the present.
In New Mexico the San Luis basin is bounded
much as 1,750 feet thick (Montgomery, p. 53),
glomeratic
redbeds
of
early
to
middle
Tertiary
The eastern and northern boundaries of the at the west by the gently east-tilted Brazos uplift
and it rests on Precambrian and Pennsylvania!!
Jfc'e.
San Luis basin are the complex zones of high- The boundary is obscured by volcanic rocks anil
rocks. Patches of conglomeratic redbeds of probangle f a u l t s at the western margin of the Sangre sediments of late Tertiary and Quaternary ages,
able early Tertiary age thai are overlain by thick
ROCKS OF K A K L Y TO M 1 U U L K T K K T I A R Y AC.E
ile Cristo u p l i f t . These faults are concealed at b u t , at the south at least, the western boundary
In the southern part of the Brazos uplift Pre- volcanic rocks of early to middle Tertiary age lie
most places by Quaternary fans and pediment
of the basin is marked by large normal faults
amhrian
rocks are overlain by (he El Rito For- unconformably on Precambrian rocks high in the
deposits. The northern part of the u p l i f t is linked downthrown to the east (Kelley, 195d, p. 110;
mation of Smith (1938) of Eocene( ?) age. Sangre de Cristo uplift north of Taos (McKinaround the narrow northern part of the basin, 1954). This southern part of Ihe basin west of
These rocks consist of pebble to boulder con- lay, 1956, p. 12-15). In the Culebra Reentrant
w i t h the Sawalch and Gunnison uplifts. The Taos is a graben. The southern boundary of the
glomerate, red shale, and sandstone, and they are redbeds of the Vallejo Formation (Upson, 1941),
western part of the basin in Colorado merges into San Luis basin was defined by Kelley (1956, p.
tiniilar to their probable correlative, the Blanco probably early Tertiary in age, are overlain by
(lie east-tilled Del Norte structural sag (Atwood
10'J) as the Embudo structural constriction
Basin Formation of Oligocene( ?), and possibly volcanic rocks probably equivalent to the Potosi
and Malher, 1032, p. 24 and PI. 2) on the eastern where, at Cerro Azul, a fault block of PrecamEuccne, age (Larsen and Cross, 1956, p. 60-61) Volcanic Group. These rocks probably are generllank of the complex uplift of the San Juan brian rocks rises as an "island" through Tertiary
thich rests on rocks of Cretaceous age at out- ally equivalent to the Picuris Tuff of Cabot
Mountains region (Larsen and Cross, 1956, p.
and Quaternary sediments and basalt flows. At
aops in the northern part of the Brazos uplift (1938; Upson, 1941, p. 587). The Vallejo and
243-244 and Pis. 2, 4). Possibly this margin is the eastern edge of the basin, along Ihe Rio
«id the southernmost part of the San Juan overlying volcanics likely are equivalent to the
marked locally by faults downlhrown to the eas>, Grande east of Cerro Azul, sharply tilted TerMountains volcanic field. The El Rito is as much early Tertiary redbeds and overlying volcanics
but the relations are obscured by Quaternary sed- tiary sediments and local angular unconformities
fc 200 feet thick, and the Blanco Basin is mapped north of Taos by McKinlay.
iments including a huge, topographically low fan show that the basin subsided in several stages
These relations seem to indicate that the Santa
fiO-500 feet thick.
built by the Rio Grande (Siebenthal, 1910, p. 10; along a well-defined fault zone (Montgomery.
Fe
Group in the southern part of the San Luis
The El Rito and Blanco Basin Formations are
Powell, 1958, p. 11 ).
1953) at the western edge of the Precambrian
basin is underlain by a sequence of sedimentary
overlain
by
thick
series
of
rhyolitic
to
latitic
How
The structural segment of the basin that in- rocks of the Picuris Mountains prong of the
neks, volcanic conglomerate, and tuff. At the rocks and latitic to rhyolitic volcanic rocks of
cludes the physiographic Alamosa Basin seems to Sangre de Cristo uplift. In the vicinity of Taos,
»uth the volcanic rocks are assigned to the early to middle Tertiary age that may be as much
la- a northeast-tilted, warped block whose trough Pennsylvania!! rocks of the u p l i f t are adjacent to
Abiquiu Formation of Smith (1938) and the Car- as 2,000 feet thick, and that probably rest on
probably is near the fault boundary with the the eastern faulted border of the San Luis basin.
son Conglomerate of Just (1937), both of Mio- mainly Precambrian rocks. Possibly, PennsylvaSangre de Crislo u p l i f t . This probably is the On the north, Precambrian rocks of the uplift arc
structurally deepest part of the San Luis basin.
.'070
2071
RATON AND SAN LUIS liASINS
ELMKR H. UAI.TZ
EXPLANATION
Fan and pediment deposits,
and Alamosa Formation
Potosi Volcanic Group
and, locally.some
pre~ Potosi rocks
Carson Conglomerate
Just (1937)
and Abiquiu Formation
ot Smith (1938)
Volcanic rocks,
related intrusives and,
ot the base, variegated
conglomerate, sandstone,
ond shale. Includes the
Vollejo Formation of
Upson (1941) and overlying pre-Hinsdole
volcanics in Colorado
o
ax
o: o
o3
Geologic mop compiled mainly from 1
U . S G e o l . Survey, 1935
Dane ond Bachman, 1957
Dane and Bachman, 1962
Larsen and Cross, 1956
BIOGRAPHIC DIVISIONS
lUPSON, 1939, F I G 2)
1 ni> basin and adjacent regions.
E . H . B a l t z , 1965
RATON AND SAN LUIS BASINS
ELMER H. BALTZ
an rocks are present lieneath the early Tertiary
i Us in the vicinity of Tacs.
In the northern part of the basin volcanic
i ks including (he I'otosi Volcanic Group and
inn- pre-Polosi volcanic rocks dip east from the
an Juan Mountains anil pass beneath Quaterary sediments and the Santa Fe Croup in the
iisin. The Orrin Tucker No. 1 Thomas well in
re. 13, T. 41 N., R. 8 E.. about 24 miles north\est of Alamosa, encountered a sequence of
nainly volcanic conglomerates and breccias and
-iime flow rocks between the depth of 5,210 feet
md the total depth of 8,023 feet. These rocks
probably are mainly the Potosi Volcanic Group,
but the lower 173 feet contain much red, purple,
ami green clay similar to the lilanco Basin Formation (see log in 1'owell, 1958, p. 275-2HO).
In most of the northern part of the San Luis
basin it is impossible to say what lies beneath the
volcanic rocks which may be 3,000-4,000 feet
thick at places (Larsen and Cross, 1956, I'l. 2).
Perhaps Mesozoic rocks are present beneath the
volcanics west and northwest of Alamosa (Larsen
and Cross, 1956, I'l. 2. cross sections B-B' to E-E')
as they are in the southern part of the San
Juan Mountains, but there are no outcrops or
well data to provide clues regarding the distribution of the Mesozoic rocks. Near the northern
end of the basin the volcanics rest on uplifted
and faulted Precambrian crystalline rocks and
Paleozoic sedimentary rocks. The sedimentary
rocks probably are on the southwestern margin of
the ancient Central Colorado basin, and would
not be expected to be present farther south in the
area of the ancient San Luis uplift, part of which
is in the San Luis basin (Fig. 2).
The eastern part of the San Luis basin was, in
Paleozoic time, part of the Central Colorado
basin. However, the Precambrian rocks at the
western side of the Sangre de Cristo uplift rose
from the ancient basin during Laramide orogeny.
It seems almost certain that, prior to the downfaulting of the Rio Grande trough, the area of
much of the eastern San Luis basin was part of
the generally mountainous region that constituted
the hinterland of the Laramide erogenic belt.
Therefore, it is unlikely that any extensive areas
of Paleozoic or Mesozoic sedimentary rocks are
preserved in the subsurface of the eastern San
Luis basin except possibly in fault slices.
SEDIMENTS AND ROCKS Of MIDDLE TERTIARY
TO QUATERNARY!?) AGE
Santa l!e Group cmd equivalent rocks and sci/imcH/s.—The Santa Ee Group of middlef?) Miocene to Vleistocene(?') age is a syntectonic deposit that fills nearly all the Rio Grande trough
The Santa Ee Group consists of several intergrading units of sediments, volcanic detritus, anil
basaltic and andesitic flow rocks. The lowest unit
is composed of pinkish buff and gray sand, sill,
local gravel, local tuffaceous sediments, and a few
basalt tlows. These deposits were named the
Tesuque Formation of middlet?) Miocene to
early Pliocene age by Spiegel and Ualdwin (196.?.
p. 39-45). In the San Luis basin the Tesuque Formation is exposed in the gorge of the Rio G ramie
southwest of Taos and along the southeastern
margin of the Brazos uplift.
The Tesuque Formation is overlain by a sequence of basalt and andesile tlows and interbeililed thin sediments of Pliocene and Pleistocene;?) age that extend across the Taos Plateau in
the southern part of the basin and are at leaM
500 feet thick northwest of Taos. The basalts and
andesites of the Santa Ee Group were erupted
from centers that rise as hills above the plains on
both sides of the Rio Grande. At the western
margin of the basin in New Mexico the flows lap
across the Tesuque Formation onto the Carbon
Conglomerate. In southern Colorado the basalt?
and andesites are referred to the Hinsdale Formation (Larsen and Cross, 1956") and they lap
onto the Potosi Volcanic Group which crops uut
in the north-trending San Luis Hills west of the
Rio Grande for about 20 miles norlh of the Stale
line. The tlows also lap onto the Potosi at the
western margin of the Alamosa Basin and artpresent in the subsurface southwest of Alamos
where they dip northeast in the Alamosa lia^n
beneath the Quaternary sediments (Powell, 1951
p. 19) and wedge out or become thin and discontinuous northeastward.
In the Alamosa liasin north of Alamosa, sail
ments that are mainly equivalent to the Tesuijuc
Formation and basalts that are equivalent to the
Hinsdale Formation have been penetrated in deep
wells. These sediments are predominantly piitohbuff but contain gray, red, and bluish beds. The
Tesuque consists of clay, arkosic sand, and grau!
(hat are slightly calcareous, and the formation
207,?
contains some beds of tuffaceous material and the "sump" area of the Alamosa Basin between
volcanic conglomerate. The sediments were de- Alamosa and Moffat, in an area about 30 miles
rived from the granitic terrane of the Sangre de long and 8 miles wide. Here, water produced
Cristo uplift and also from the San Juan Moun- from the Alamosa Formation between depths of
tains volcanic field. The Orrin Tucker No. 1 160 and 1,018 feet is organically tinted and conThomas well penetrated about 885 feet of Quater- tains small amounts of gas which was used at
nary sediments and about 4,325 feet of sediments places for domestic purposes. Siebenthal reported
which are referable mainly to the Tesuque For- that the sediments of the Alamosa Formation
mation. An undetermined amount, perhaps 600 contain organic material in this area and indifeel, of the upper part of (he Tesuque probably 1'ileil that these organic sediments originated in a
is laterally equivalent to the basalt and andesile lacustrine environment in the deeper part of the
llows ((he Hinsdale Formation) of the upper part basin and probably were the sources of the gas.
of the Santa Fe Group south of Alamosa.
CONCLUSIONS
"Shows" of gas were reported at depths of 3,801
feet and 4,006 feet in the Tesuque Formation at
In middle Tertiary time, after the extrusion of
the Rush and Calvert well in sec. 27, T. 41 N., large amounts of volcanic material of mainly inK. 10 E., about 25 miles north of Alamosa. 'I h s termediate composition in Laramide orogenic
gas may have been volcanically generated,.or it areas of north-central New Mexico and south-cenmay have been "swamp gas" from buried carbo- tral Colorado, the Laramide geanticline (hat innaceous sediments. The tluviatile and playa-type cluded the eastern part of the ancient San Luis
sediments of the Tesuque Formation are not like- uplift and the hinterland of the Sangre de Crislo
ly sources of petroleum.
uplift was tilted eastward. Its eastern part foundered along high-angle faults to form the complex
SEDIMENTS OF LATE TERTIARY AND
faulted blocks of ihe San Luis basin. This eastQUATERNARY ACE
tilting and downfaulting continued episodically
The Alamosa Formation of Pliocene or Pleisto- through the late Tertiary and was accompanied
lene age (Siebenthal, 1910, p. 40-47; Powell, by deposition of the Tesuque Formation and ex1058, p. 20-24) overlies the Santa Fe Group in trusion of basalts and andesites. Some of the deColorado and consists of unconsolidated gravel, formation and basin filling continued into the
Maud, silt, and clay. These sediments are confined Quaternary period.
mainly to the Alamosa Basin, but thinner equivaBecause the region of much of the San Luis
lents are present in (he Cost ilia Plains in New basin was part of the ancient San Luis uplift and
Mexico, also. The coarser materials were depos- was a source terrane for a tremendous amount of
ited near the margins of the Alamosa Basin as sediment shed both east and west in late Paleozotans, and finer material was deposited, probably ic time, part of Mesozoic time, and latest Cretain a lacustrine environment, in the eastern part of ceous and early Tertiary time, it is doubtful that
the basin in the "sump" area where the present e.xteisive arc's of Paleozoic or Mesozuic r:>ck;
lakes and playas occur. Records from deep water are preserved in the basin beneath (he Tertiary
wells indicate that the Alamosa Formation ranges vo'canics and basin fill. This conclusion is indiin thickness from a feather edge at the western cated also by outcrops in northern New Mexico
side of the basin to more than 2,000 feet in the where Tertiary sediments and volcanics rest on
central part of the basin north of Alamosa.
the Precambrian west of the basin, at places
The Alamosa Formation is overlain by allu- within the basin, and in the western part of the
vium and, on the margins of the basin, by Pleis- Sangre de Cristo uplift. Possibly, Pennsylvanian
tocene to Recent fans and pediment gravels and, rocks are present beneath the early Tertiary
locally, dune sand. Quaternary fan deposits form rocks in the basin near Taos. Although small
the surface of most of the basin in the Costilla amounts of ''swamp gas'" occur in Pliocene and
Plains east of the Rio Grande in New Mexico.
Pleistocene sediments, the stratigraphy and geoSiebenthal (1910, p. 81-90) reported and dis- logic history of the San Luis basin are not encourlussed the occurrence of flammable natural gas in aging for possibilities of petroleum occurrence.
RATON AND SAN LUIS HAS1NS
ELMER H. BALT2
2074
1960, The boundary between rocks of Carlilt
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!•*•*•*, LjLiuii^iui»ij
_.
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• • D• ..• _structure
---...
«--.-i..in ^^
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S
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§
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