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ESSENTIAL QUESTIONS TO ASK
Arizona.1 Introduction
What role has plate tectonics played in creating Arizona’s landscape?
What are the three physiographic provinces found in Arizona?
Arizona.2 The Proterozoic Foundation of Arizona
What primary process was involved in forming the land in Arizona’s early history?
Where do we see Proterozoic rocks exposed in the state today?
Arizona.3 Paleozoic Clastics and Carbonates
What evidence do we have that several episodes of transgressions and regressions
deposited thick sedimentary sequences?
ons that covered Arizona?
How extensive were the marine inundations
Arizona.4 Transitions during the Mesozoic
sozoic E
Era
c
the northeastern
north
portion of
Why were there extensive sand and river deposits covering
the state?
nic deposits
depos in southern Arizona?
Ar
Where were the sources for volcanic
Arizona.5 Laramide and
d Mid-Tertiary
Mid-Ter ar Upheaval
aval
te tectonics play in creating geologic
eolog features in Arizona?
What role did plate
Arizona.6 Volcanic Activity
re the timee span and
an spatial extent
tent of volcanism?
What are
volcanic features have
ve been
bee formed?
Whatt types of volca
Arizona.7 Formation of the Grand Canyon
w did the Colorado
Co
River
er form
for the Grand Canyon?
How
id aall the eroded
ed material
ma
go?
Where did
dynamic is thee Grand
Gran Canyon in terms of changing in the future?
How dyn
Arizona. Economic
Arizona.8
ic Resources
Re
Why is Arizona hhome to some of the largest copper deposits in the world, and how
W
have
contributed to the development of the state?
ave they cont
What does the future hold for mining in the state?
Arizona.9
9 Water R
Resources
Where does Arizona get its water?
What is the future of water in Arizona?
Arizona.10 Environmental Concerns and Geologic Hazards
Arizo
Has Arizona experienced natural disasters in the past?
How stable is the state in terms of future disasters?
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author(s). Geology of Arizona/David M. Best - First Edition ISBN 1-426-62628-2. Printed in the United States of America.
Geology of Arizona
Eon
Era
Period
Epoch
Recent or
Holocene
Tertiary
Paleogene
Cenozoic
Neogene
Quaternary
Carboniferous
erou
Mesozoic
Paleozoic
oic
Phanerozoic
0
Pleistocene
0.01
Pliocene
1.8
Miocene
5
Oligocene
23
Eocene
Eoce
34
Paleocene
Paleo
56
Cretaceous
66
Jurassic
146
Triassic
c
200
Permian
Permia
251
Pennsylvanian
n
299
Mississippian
ssissip
318
Devonian
De
359
Silurian
416
Ordovician
444
Cambrian
488
Proterozoic
c
As a student taking a geology course in Arizona, you will
want to learn how the concepts you become exposed to can
be applied to the rich and diverse geologic settings within
the state. The overview that follows takes you across the
state in terms of its geology, addressing some of the major
topographic differences as well as the wide variety of rock
types and the manner in which they were formed and subsequently exposed.
Many people think of Arizona as being covered only by
desert, with the Grand Canyon somewhere within the state
boundaries. Located in the American Southwest, Arizona
has a wide range of rock types, including some that formed
almost 2 billion years ago (Ga). The northern and northeastern portions of the state are covered by relatively horizontal layers of sedimentary units, which formed near
continental margins, in shallow seas, or in desert conditions.
Portions of the southern and southwestern regions are the
result of tectonic activity that occurred between 30 and
80 million years ago (Ma). Throughout the state, igneous
activity produced several dozen mountain ranges and areas
ic
of extrusive material. We will refer to various geologic
times throughout our discussion, so the geologic time scalee
ion for
is provided to help you gain a temporal appreciation
).
when different events occurred (Figure Arizona.1).
The overarching concept of plate tectonics, a theory that
has become well established in geology since the ear
early
ng the way the
he st
1960s, has been instrumental in explaining
state
eup of the So
looks and in contributing to the makeup
Southwest.
ceans and the uplift of
The effects of major incursions of oceans
ing land, co
th
mountain ranges and the surrounding
coupled with
es, hav
collisions between landmasses,
havee all lef
left their mark.
gic tim
Arizona has moved across the globe thr
through geologic
time,
which helps explain the formation of m
major rock units such
tone dep
d with marine
as limestone and sandstone
deposits associated
nmen , respec
sions with other
and desert environments,
respectively. Collisions
d vo
nd ig
plates produced
volcanic extr
extrusions and
igneous masses
w the surface.
surf
he C
buried below
During the
Cambrian Period,
a
gree north of the equaArizona wass situated at about
10 degrees
onm
tor, where shallow marine environments
created lime muds
(Figure Arizona.2).
The region then began to move to the south until the
en it
i began its long journey northmid-Silurian Period, when
ward. This steady movement has seen it shift from roughly
20 degrees south latitude to as far north as 45 degrees,
which lies along the present-day Montana-Wyoming border.
During this time the region experienced a wide range of
geologic environments. Today Arizona is located at approximately 35 degrees north of the equator.
Keep in mind that most of the current topography has
been carved by weather and climate over a relatively short
time span (several tens of millions of years) when measured
against the age of the oldest exposed rocks or even the age
of the Earth itself, estimated at about 4.6 billion years.
Figure Arizona.1 Geologic time scale. The numbers indicate the
number of years before present, in millions of years.
542
Archean
Arizona.1
Introduction
2500
Hadean
Arizona
Precambrian
2
3600
Early bacteria
4600
Exposed outcrops display areas that were once located at
the depositional terminus of major streams that eroded
nearby mountains, creating extensive deposits of mudstones, sandstones, and conglomerates.
The Geologic Map of Arizona and
Physiographic Provinces
A physiographic province is a region in which all parts
display similar geologic structures and geomorphology.
When the concept is applied to Arizona, there are three
such provinces within the state (Figure Arizona.3).
Arizona.1 Introduction
Figure Arizona.2 The Southwest was covered by shallow
equatorial seas during the Middle Cambrian. Extensive shallow waters
covered most of Arizona and regions to the north and west. Deeper
oceans are shown to the west and continental landmasses to the east.
The northern third of the state lies in the Colorado
Plateau, a relatively circular area centered on the Four
Corners region (the only point in the United States where
four states come together—Arizona, New Mexico,
Colorado, and Utah). Rocks on the Colorado Plateau in
Arizona are predominantly sedimentary units consisting of
sandstones, mudstones, and limestones (Figures Arizona.4
and Arizona.5). Most of the rocks range in age from
Permian to Triassic, with lesser amounts of Cretaceous
Image by Dr. Ronald C. Blakey, Northern Arizona University.
Figure Arizona.4
izona.4 Sedimentary rocks are
re common
co
in northern
M enkopi Formation
F
d in continental rivers and
Arizona. The Moenkopi
formed
epicontinental
ontinental seas.
se s
Figure Arizona.3 The physiographic regions
reg
of Arizona.
na.
CO
PL LOR
AT AD
EA O
U
TR
AN
S
IT
IO
N
ZON
E
BAS
IN A
ND
RAN
GE
3
Figure Arizona.5 The Kaibab Limestone, as seen from the Little
Colorado River Scenic Overlook east of the Grand Canyon, displays
layered strata that formed in a shallow, warm water sea that existed
during the Permian Period.
4
Arizona
Geology of Arizona
sediments cropping out in localized areas that contain sandstones interbedded with coal and shales. There are also
some volcanic rocks that form small mountain ranges and
isolated peaks.
Moving to the south we encounter the Transition Zone,
a region that serves as the dividing line between the rocks
of the Colorado Plateau and those of the Basin and Range
physiographic province to the south and west. Within the
Transition Zone lie many of the oldest exposed rocks found
in the state. In general the oldest rocks are found in the
northwest part of the Transition Zone. Some samples found
north of Kingman are about 1.8 billion years old. These
rocks are thought to have been part of a continental mass
associated with the earliest formation of the North
American continent, which contains the Wyoming
Province, an area that extends to the north and east from
northern Arizona across Wyoming and the Dakotas.
Collisions of these landmasses produced intrusive igneous
and metamorphic rocks that are common in the mountains
of northwest Arizona and southeastern Nevada. To the
southeast there are exposures of granites and metamorphic
rocks that formed from about 1.6 to 1.4 Ga.
The Basin and Range Province includes a large number
of alternating mountain ranges and valleys that lie along the
n
western edge of Arizona, extending across the southern
d
reaches of the state into southernmost New Mexico and
west Texas. These features formed during the plate tectonic
activity associated with the Laramide Orogeny, a mountainbuilding event that had a profound effect on the geology of
ning abo
ut 75 to
most of the western United States beginning
about
ly 25 to 30 mil
80 million years ago and lasting roughly
million
quit varied.
years (Figure Arizona.6). Ages of these rocks are quite
Small outcrops of Proterozoic rockss are interspe
interspersed with
d T
rtiary sedim
larger masses of Paleozoic and
Tertiary
sedimentary and
volcanic units.
Section Arizona.1 Summary
Arizona has had a complex geologic history, which is
recorded in a diverse range of rock sequences and
surface features.
The state is divided into three physiographic regions,
each having a distinct geologic history and appearance.
Arizona.2
The Proterozoic
oic Foundation
Found
n
of Arizona
Figure Arizona.6
ona.6 Mountain
Mo
ranges consisting
sting of igneous and
sedimentary rocks are common
as seen in the
comm in southern Arizona,
Arizo
Muggins Mountains,
ntains, east of Yuma. This region
egion is located in the Basin
and Range Province.
Photo by W. Sylvester Allred.
The central part
rt of the Nort
North American crat
craton is composed
al lithosphere that formed
ed b
of continental
by the suturing of
er continent
several smaller
continental masses mo
more than 2 Ga. In the
west
United States several
vera episodes of accretion
southwestern
urred that ad
occurred
added multiple terra
terranes to the 2.5-billion-yeard Archean Wyoming
W
ovinc over a period of 200 million
old
province
ears beginning
beginni about 1.8 G
years
Ga. The final result was a wide
exp
se of continental
tal m
expanse
material being added to the southern
edge off the craton.
on. T
The far northwest corner of the state
lies in the Mojave
ojave Province, a region that has been determined to bee old
older than areas to the south and east. The
oldestt rock u
unit in the state is the 1.84-billion-year-old
Elves Chasm quartz diorite that is exposed in the bottom of
Grand Can
Canyon and underlies portions of northwestern
Arizona.
Many o
of the oldest rocks are buried deep beneath thoud of feet of sedimentary and volcanic layers that are
sands
pervasive throughout the state. Exposed Proterozoic rocks
are predominant in the northwest and central regions of the
state, forming the bulk of the mountains that exist in the
Transition Zone, but they are found elsewhere in smaller
outcrops. In general, Proterozoic rocks in the northwest
and far southwest are sedimentary in origin; those in the
center tend to be volcanic; and the disjunct outcrops in the
southeast originated in a combination of volcanic and sedimentary environments.
Moving to the southeast through the Transition Zone,
the Yavapai Province encompasses the central portion of
this region. Its boundary with the Mojave Province is based
on a range of isotopic compositions. These two provinces
are thought to have joined by a collisional event, but no
clear evidence exists to confirm this hypothesis. The
Yavapai Province is composed of several blocks that are separated by fairly distinct fault and shear zones. Metavolcanic
and intrusive igneous rocks are common due to the existence of an island arc setting during continental collision.
Examples of these rock types are found in the PrescottJerome-Dewey area in central Arizona (Figure Arizona.7).
These large, constructional blocks extend to the southeast
where they abut the Mazatzal Province, the third of the
provinces in the Transition Zone.
Arizona.2 The Proterozoic Foundation of Arizona
Figure Arizona.7 Continental assemblages consisted of large
blocks being sutured onto preexisting continental masses. The
Bradshaw Mountains in central Arizona lie along one of the
boundaries of accreted blocks that were emplaced during the
Proterozoic Era.
The Mazatzal Province is an area that consists
ts off rock
rocks
66 to 1.6
from a wide range of sources that formed 1.66
1.60 Ga.
Events that produced the deformation in thiss province are
nental ma
thought to have been associated with a continental
margin
that lay to the south of the slightly older Yavapai Province.
ocks in this region
region indiA preponderance of granite-rich rocks
ng in the
cates the cooling of magma bodies that wer
were rising
ng place.
crust while continental collisions were taking
der fields are seen in portions of
Outcrops of granite boulder
dally weathcentral Arizona. These fields consist o
of spheroidally
n age (Figures
ered granites that are Middle Prot
Proterozoic in
b).
Arizona.8a and 8b).
in range
zoic aage are found in
Several mountain
ranges of Proterozoic
zona. Among them
th
central Arizona.
are thee Ma
Mazatzal Mountains,
5
Figure Arizona.8b This Middle Proterozoic age is located north
of Mesa along Arizona Highway 87. Extensive outcrops of boulders
cover the surface. Note the spheroidal shape of the exposed rock.
which extend south of Payson to the northeast side of
wh
Phoenix. This mountain range consists primarily of
Ph
quartzite, a ver
very hard metamorphic rock that formed originally ass a sa
sandstone. Four Peaks, a prominent feature in the
thern part of the Mazatzals, is readily visible from the
southern
Phoen
Phoenix metropolitan area (Figure Arizona.9).
Figure Arizona.9 Four Peaks, a prominent physiographic feature
east of Phoenix, is a roof pendant that is roughly 1.45 billion years
old. It is part of the larger metamorphic terrane of the Mazatzal
Mountains that extend north to Payson.
Figure Arizona.8a
Figu
na.8
Granite boulder
oulde field located near MP 259 on
of the larger Middle Proterozoic
Interstate 17. These rocks are part o
that crop out across the center of the state.
granites tha
Section Arizona.2 Summary
Three metamorphic provinces, the Mohave, Yavapai,
and Mazatzal, record the accretion of new terrane to
form central Arizona between 1.6 and 1.7 Ga.
Metamorphic rocks are the predominant rock type in
the northwest and central regions of Arizona.
6
Arizona
Geology of Arizona
Arizona.3
Paleozoic Clastics and
Carbonates
Following the formation of Proterozoic basement throughout the northern and central parts of Arizona, there is a
major period of missing time observed when we look at the
contact of the units of the Cambrian Period lying atop the
Middle and Late Proterozoic rocks seen in eastern and
central Grand Canyon. In the canyon the Cambrian
Tapeats Sandstone unconformably overlies the older
Proterozoic rocks that crop out along the Colorado River
(Figure Arizona.10a). In central Arizona, along the East
Verde River north of the city of Payson, the Cambrian
Tapeats Sandstone unconformably overlies Early Proterozoic
granites (Figure Arizona.10b). Similar conditions exist to
the southeast through the Transition Zone.
The record for Paleozoic Era rocks is quite widespread.
Rich in fossils and displaying a wide range of clast types and
sizes, these rocks afford us an excellent opportunity to
determine the environments of formation of major outcrops across the state. Depositional environments include
areas of shallow marine waters, continental river deposits,
efar-reaching deserts, and even extended periods of nondeposition caused by topographically elevated surfaces.
rmed in
The earliest units in the Paleozoic are those formed
the Cambrian Period, which ranged from 542 to 488 milhe equa
lion years ago. The state was situated between the
equator
ter se
and 10 degrees north latitude. Shallow, warm-w
warm-water
seas
entered the state from what are now the northw
northwest and
overed portion
south-central regions. Deposition covered
portions of the
state with sediment as thick as 450 meters (1,500 feet). Onee
cally
area was spared deposition, duee to itss being top
topographically
Figure Arizona.10a
0a The
e Tapeats Sandstone is a widely
wide spread
lowe boundary
dary of the Paleozoicc rocks
rock in central
unit that marks the lower
and northern Arizona.
ona. It representss the
t lowest of the relatively horizontal sedimentaryy deposits in Grand Canyon.
Figure Arizona.10b Along the East Verde River north of Payson,
exposures of the horizontal Cambrian Tapeats Sandstone unconformably overlie Proterozoic granites (seen to the right). About 800
million years is missing along this unconformity.
igh. The D
high.
Defiance Positi
Positive area, which persisted for
al
most 300 million years along the current Arizona–New
almost
Mex
co b
ows n
Mexico
border, shows
no evidence of deposition (see Figure
Arizo
Arizona.2).
IIncluded in th
the basal rocks that form the basement or
pinning of the stratigraphic column is the Tapeats
underpinning
Sandstone. T
The Tapeats, which ranges in thickness up to
110 meters
meters, formed in fluvial, beach, and tidal settings.
Deposite
Deposited on the older erosional surface of the underlying
Proterozo
Proterozoic igneous and metamorphic units, its variable
thick
thickness reflects the undulating topography of the period.
The oldest portions lie in the northwestern part of the
state, where the Tapeats crops out in Grand Canyon, and is
recognized there as the lowest of the many horizontal sedimentary units. Deposits of the Tapeats extend to the south
and east, where it is Middle Cambrian in age in the vicinity
of Roosevelt Lake. Due to its make up of feldspar-rich
sandstones and more pure quartz arenites, the Tapeats
forms a resistant ledge in the arid climate of Arizona.
To the southeast the time-equivalent unit is the Bolsa
Quartzite, which forms an unconformity in that region
over Middle Proterozoic rocks, including the Pinal Schist,
the Dripping Spring Quartzite, and the Troy Quartzite.
The Bolsa, a Middle Cambrian unit, ranges between 3 to
250 meters thick. As in the case of the Tapeats, this even
wider range of thicknesses is attributable to the paleotopography of that part of the state at the time of its deposition.
The southeastern corner of Arizona displays outcrops of
the 250-meter thick Abrigo Formation, a unit that includes
mudstones, silica-rich carbonates, and limestones. These
units formed in intertidal marine conditions that allowed
the chemical precipitation of carbonates that produced a
thick sedimentary sequence. To the southeast of the Abrigo
are deposits of the Coronado Sandstone, which reaches a
thickness of 190 meters in some localities.
Arizona.3 Paleozoic Clastics and Carbonates
Note that the carbonates, such as those found in
the Abrigo, are chemically derived and settle out from
marine waters. We will see this set of conditions again in
the Mississippian Period when the state once again lay
astride the equator and massive limestone deposits formed in
the warm-water conditions. Carbonates, especially calcium
carbonate, do not readily dissolve in warm water. Today’s
modern analog is the deposition of carbonates and the
creation of carbonate coral reefs in equatorial regions, such
as the Caribbean Sea or the Great Barrier Reef off the
northeast coast of Australia.
During the Ordovician Period, Arizona was situated at
the equator. Depositional environments during this time
produced rocks that are much less widespread. The few
exposed rocks of Ordovician age lie in the southeastern corner of the state, where the marine El Paso Limestone conformably overlies the Cambrian Abrigo Formation in the
Swisshelm and Pedrogosa Mountains.
We often think of Arizona as having a fairly complete
ar
rock record, but upon closer examination, we see it is far
socifrom complete. For example, there is no rock record associhere in
ated with the Silurian Period (444 to 416 Ma) anywhere
the state. How could this happen? One of several possible
sets of conditions could have taken place. The entire region
encould have been elevated above sea level, and any sedim
sedimenass could h
tary rocks that formed on the continental mass
have
been eroded, eventually ending up in the oceans. Als
Also the
tion that prev
region could have been at an elevation
prevented the
ans.
land from being covered by the oceans.
nown as the A
The Devonian Period is known
Age of Fishes, a
nd much of
time when extensive oceanss covered th
the glo
globe and
the land. Fish and otherr marine life were able to move
rned to ccover
freely about the oceans.. Shallow oce
oceans returned
ult off these inun
the state. One result
inundations was th
the depositin Fo
rmation a fairlyy wid
tion of the Martin
Formation,
widespread unit
ess from 0 to more than 300 meters. An
ranging in thickness
g observation is that theree is a unit in the Martin
interesting
ion
n, the Be
embe that contains fossils
Formation,
Becker’s Butte Member,
nd plants.
pl s. Give
of land
Given the fact that the Devonian was a time
hen oc
ere practically
ly ev
when
oceans were
everywhere, this “island” conterr
taining terrestrial
fossil mate
material is a rare occurrence worldwide. Thus outcrops of the Becker’s Butte Member near
Globe are unusual for ccontinental units of Devonian age.
What might hav
have produced this topographically high
esea
area? Some researchers
think that mountain-building activort
ity to the northwest
of the state could have generated sufficient forces to lift up the land in central Arizona. Orogenic
activity associated with the Antler Orogeny, a major
mountain-building episode that took place in central
Nevada, could have been contemporaneous with uplift that
allowed creation of the Becker’s Butte deposits. This is an
example of how widespread tectonic forces can affect seemingly far away regions.
Near the end of the Devonian Period, Arizona underwent a period of uplift that pushed marine deposits onto the
continent and produced higher elevations. This activity was
coupled with a retreat of the seas that had covered the
7
region. Either erosion skimmed away sediments being
formed on the land or there was a prolonged period of nondeposition. The result was a major disconformity between
the Devonian rocks and those of the overlying Mississippian
Period. Down cutting took place in the uplifted landmasses,
resulting in incised channels that occasionally infilled with
sediment.
The Mississippian Period saw another series of transgressive oceanic sequences. Arizona was still situated in
warm, equatorial waters that provided the ideal environment for calcareous mud
muds to build up. Animal and plant life
een in th
were abundant as seen
the fossil record. Once again the
tate as well as the
northwest and southeast corn
corners of the state,
watter sseas. These concentral part,, were covered b
by warm-water
on o
ditions were right ffor the production
of thick deposits of
one. Th
limestone.
Thee Miss
Mississippian Red
Redwall Limestone, a very
ominent cliff former in thee Gr
prominent
Grand Canyon, and its timequivalent unit to the south,
uth, the Escabrosa Limestone, are
equivalent
evidence of these tropical
opica depositional conditions. For
those who have hiked
ked the Grand Canyon, the Redwall
po
poses one of the majo
major climbs; the unit is a sheer cliff more
tha
rs hi
than 250 meters
high (Figure Arizona.11).
nd of the Mississippian Period, another disconAt the end
formity is obs
observed with the overlying Pennsylvanian rocks
units. Thi
This break in the rock record could be due to a
gressi
regression
or withdrawal of the equatorial seas associated
with another period of uplift. The erosion that occurred on
th
this limestone surface formed karst topography. Resting
atop the Redwall Limestone is a discontinuous series of
infilled channel deposits that were produced by an ancient
drainage system that flowed across the Redwall surface during the Late Mississippian. These lens-shaped units, which
consist of a wide range of smaller clastics and limestone,
comprise the Surprise Canyon Formation, a relatively
Figure Arizona.11 Thick deposits of Redwall Limestone (seen
in the right center) formed in a shallow marine sea that covered
northern Arizona. The Redwall, along with its equivalent to the south,
the Escabrosa Limestone, formed when the region was near the
equator.
Arizona
Geology of Arizona
recently recognized formation within Grand Canyon. Its
discovery in the mid-1980s points out that indeed change
can occur by the recognition of new units in an area that
seemingly had all its geology interpreted. Geology is
dynamic!
Following the erosional conditions that marked the end
of the Mississippian Period as time moved forward to the
Pennsylvanian, the state was once again covered by seas
that came in from the northwest and the southeast. The
central part of the state had low mountains that prevented
that area from being flooded. In the southeast there was a
continuation of deposition of limestones as the seas in that
region continued to be deep and warm enough to produce
these deposits. Portions of the far southeastern corner of
the state have as much as 650 meters (2,000 feet) of deposits
of carbonate rocks.
To the north in the central region the unit at the base of
the Pennsylvanian is the Naco Formation, which lies conformably on the Mississippian Redwall Limestone. The
Naco is typically a sand-rich series of redbeds that formed
in a continental setting as streams drained higher regions
into a shallow sea. This unit is rich in fossils as significant
beds of brachiopods, sponges, mollusks, and other invertebrates are found in outcrops to the south and east of the
n
town of Payson. The Mid-Pennsylvanian Naco Formation
in north-central Arizona consists mostly of resistant lime-te develstones, interbedded shales, and a basal conglomerate
an Redwall
oped from erosion of the underlying Mississippian
Limestone.
Section Arizona.3 Summary
Sedimentary rocks predominate the Paleozoic Era as a
ical rocks
ocks indic
ral
range of clastic and chemical
indicate several
nments.
different depositional environments.
Figure Arizona.12 During the Late Triassic Period the depositional environment of the Southwest was influenced by rivers draining
across the land and depositing continental sediments over a large
area.
Image by Dr. Ronald C. Blakey, Northern Arizona University.
8
all having been deposited in continental environments. The
Chinle co
contains numerous deposits of clays that expand and
contract when water is present. The Petrified Forest
Member of the Chinle Formation weathers to produce a
badlands type of topography (Figure Arizona.13).
Similar depositionall environments e
existed across
ross m
most
gh
h some h
n the center
of the state, although
higher regions in
experienced continental
deposits.
tinen deposi
Arizona.4
urin
Transitions during
the Mesozoic E
Era
During the Late Paleozoic Period the state experienced a
transition from shallow marine deposition to one of fluvial
and eolian environments. In the early Triassic Period,
northern Arizona saw continental rivers deposit a combination of sandstones and mudstones that are part of the
Moenkopi Formation (Figure Arizona.12). The land was
relatively flat, allowing the sediment to disperse over large
areas. Unconformably overlying the Moenkopi is the
Chinle Formation, another wide-ranging unit that consists
of mudstones and sandstones, along with some limestone,
Figure Arizona.13 View of the badlands topography in Petrified
Forest National Park, northeast Arizona. The Chinle Formation contains clays that are capable of absorbing water, which causes the
ground to expand and contract during wet periods. These units
weather and produce a wide range of gray and white hues.
Arizona.5 Laramide and Mid-Tertiary Upheaval
Figure Arizona.14 The Echo Cliffs were formed during a period
of tectonic activity that involved the creation of a number of
monoclines in northern Arizona.
9
ranges in southwestern Arizona to the east of Yuma are predominantly Jurassic intrusive plutons related to the
Cordilleran arc, with a few isolated mountains displaying a
younger Cretaceous age. The geologic setting that produced this activity is thought to be subduction of oceanic
plates of the early Pacific Ocean diving underneath the
westward moving North American plate. In southern and
southeastern Arizona a similar set of events produced many
of the rocks that are exposed in the mountains found to the
south and southwest of Tucson. Extensive strike-slip faulting caused the mountain
untai ranges to align in the general
northwest-striking trend
that is evident today.
rend tha
Section Arizona.4
Arizona Summary
mar
A combina
combination
on of fluviall an
and eolian deposits cover
nort
na, while
w
much of northern
Arizona,
to the south volcanic
predom
rocks predominate.
Subdu
Subduction of the Pacific Plate under the American
In northern Arizona, on the drive to Page, one passes
asses by
ins tthe
he clasthe Echo Cliffs, a pronounced ridge that contains
rassic Per
ods
sic units of the Upper Triassic and the Jurassic
Periods
ong with the
(Figure Arizona.14). These same units, along
younger Navajo Sandstone, are seen ass you drive along the
ob Lake and tthe North
Vermilion Cliffs on your way to Jacob
hese very
Rim of the Grand Canyon (Figure Arizona.15). T
These
d well in
ah, with
extensive sedimentary deposits extend
into Utah,
orado and New
ew Mexico.
co.
lesser amounts found in Colorado
ery differSouthern and western Arizona expe
experienced a very
ring the Meso
ent set of conditions during
Mesozoic Era. The prim
primary
or y of rocks fo
source for the majority
found in these areas was
trusiv Mountain
igneous activity, both intrusive and extrusive.
Figure
gure Arizona.15
zona.15 The Vermilion
n Cliffs
Clif display a good representation
of the Paleozoic
ion o
eozoic stratigraphyy seen
see across the northern part of
state. Rocks of the Moenkopi
are exposed at the botthe state
pi Formation
Fo
forms the uppermost surface.
tom of the ccliff, and Navajo Sandstone
ands
S
nerat a range of plutonic and volcanic
Southwest
generated
r
rocks
in the state
state.
Ari
Arizona.5
Laramide and Mid-Tertiary
Upheaval
Mountain-building episodes have affected the state in many
ways. We saw earlier how the Antler orogeny in Nevada
played a role in rearranging the landscape of the region
during the Paleozoic Era.
During the Late Cretaceous into the Early Tertiary
Period there was extensive plutonism and deformation
associated with the Laramide Orogeny, an event that produced effects from Wyoming and Idaho southward to the
western and southern portions of Arizona. Typical crustal
movement involved large blocks being uplifted in a nearly
vertical manner, with some reverse faulting occurring as
well. This movement served to reactivate preexisting largescale fractures in the deeper Proterozoic rocks. Paleozoic
rocks that had been deposited on the Colorado Plateau in
northern Arizona were often flexed or folded to produce
monoclines (Figure Arizona.16). Excellent examples of
these folds are seen in the area surrounding Grand Canyon.
The East Kaibab monocline runs basically north-south
through the eastern portion of the canyon. As you drive
along U.S. 89 to Jacob Lake and the North Rim, the highway ascends across the single flexure of the landscape produced by this monocline.
Another product of the Laramide Orogeny was the
formation of widespread plutonic bodies in southern and
western Arizona. Many of the features are now exposed following erosion of the overlying surface material, thereby
10
Arizona
Geology of Arizona
Figure Arizona.16 Block diagram showing a monocline. Note
the gentle flexure that bends the rocks, lifting one side over the other.
Due to the brittle nature of the rocks, small fractures are associated
with the bending process.
35
producing significant outcrops of granites and granodiorites. Igneous activity, along with uplift, appears to have
moved from west to east. To the west of Globe and Miami,
extensive outcrops of granites are seen. These formed during the early and middle stages of the Laramide Orogenyy
and serve as sources for some of the large copper depositss
s, located
found in southern Arizona. The Tucson Mountains,
west of Tucson, consist of volcanic tuffs formed by igneous
activity related to the orogeny.
The Rincon Mountains and the Santa Catali
Catalina
Mountains east of Tucson are part of a metamorp
metamorphic core
complex. These features are formed by thrusting aand uplift
uring the M
ry
of Proterozoic granitic-like domes during
Mid-Tertiary
ation
Orogeny, about 30 Ma. Moun
Mount Lemmo
Lemmon, elevation
he highe
2,791 meters (9,157 feet), is the
highest point in thee San
Santa
he are
Catalinas, which is the most prominent range in the
area.
o Late Cretace
During the Early to
Cretaceous the lands
landscape in
thwe tern Ar
northern and northwestern
Arizona was affect
affected by the
arpin of the crust
Sevier Orogeny. The
There was som
some down warping
o no
that extended from so
southern Utah into
northern Arizona.
oded with marine waters
These lowerr lying areas b
became flooded
he Western Interior
nter Seaway of the Late
and formed part of the
tone and mudstones reached
Cretaceous. Deposits of sandstones
thicknesses of 100 meters. Wit
Within these units lie coal beds
that are mined in the Blac
Black Mesa region of the Navajo
Reservation.
Section Arizona.5 Summary
Cretaceous seas covered northeastern Arizona. Condi-
tions were right for the formation of extensive coal
deposits.
The Laramide Orogeny created numerous folds and
faults throughout Arizona as well as numerous plutonic
structures.
Arizona.6
Volcanic Activity
Evidence of volcanic activity can be found in all parts of
Arizona. Most of the activity took place after the Laramide
Orogeny, with the majority occurring from about 25 Ma to
13 Ma. More than two dozen volcanic fields are associated
with mountain ranges across the state; these are found in
the Basin and Range and Transition regions. The entire
oli fields is spread relarange of basalt to andesite to rhyolite
gions.
tively evenly across these two regions.
m
Extrusive structures that have formed included numericularly promin
orthe
ous cinder cones, particularly
prominent in northern
hen cin
ateri are
Arizona. These form when
cinders and loose material
ose prox
ejected and build up in clo
close
proximity to thee ce
central vent.
o not last long in the geo
Such features do
geologic record
re not held to
ava. There are some
because they are
together by lava.
nder cones, such as the
basaltic flows associated wi
with these cinder
low found at the base of S
Bonito lava flow
Sunset Crater north of
taff ((Figure
ure Ariz
Flagstaff
Arizona.17). Strat
Stratovolcanoes are found in
es res
the state. These large features
result from a series of ejected
oose debris an
ws th
loose
and lava flows
that build up a conical-shaped
mountain.
mong the best know
Among
known mountainous areas are the San
Franc
Francisco Peaks nort
north of Flagstaff, the White Mountains
n east-central
ea
al Ari
in
Arizona, and the Chiricahua Mountains in
ast co
the southeast
corner of the state. To the east of Phoenix
lies the Gold
Goldfield Mountains along with the Superstition
Mountains
Mountains, two separate features that formed over a
15-million15-million-year period beginning about 30 Ma. Volcanic
features stretch from Bill Williams Mountain near the
town of W
Williams eastward north of Flagstaff to Sunset
Crater National Monument. A combination of cinder
cones and the stratovolcano encompassing Humphreys
Figure Arizona.17 Basaltic flow near Sunset Crater, north of
Flagstaff. This particular flow was extruded from the base of the crater
after the central vent became clogged up with pyroclastic debris.
Arizona.7 Formation of the Grand Canyon
Figure Arizona.18 The San Francisco Peaks north of Flagstaff.
The peak in the distance to the left is Humphreys Peak, the highest
point in the state at 3,851 meters (12,633 feet).
11
Figure Arizona.20 Table Mesa, an eroding hill covered by a
protective layer of basalt that is 20 million years old, lies south of
Black Canyon City.
Section Arizona.6
S
rizon Summary
Peak, the state’s highest point at 3,851 meters (12,633
2,6 3 feet)
feet),
formed over the past 6 million years (Figuree Arizon
Arizona.18).
8).
Other areas of the state have volcanic deposits,
osits, such as
zona (Fig
the Peach Springs tuff in western Arizona
(Figure
Arizona.19).
ws play is that they proroOne role that basaltic lava flows
vent ero
duce a hard, resistant layer and prevent
erosion of softer,
urface becomes
mes brounderlying material. When the hard ssurface
treat of the u
ken, there is erosional retreat
underlying rock. The
uch as the odd
result is a small mesa, such
oddly named Table Mesa
anish means table) on
n the east side
(recall that mesa in Spanish
h of Blac
on C
of Interstate 17 sout
south
Black Canyon
City (Figure
Arizona.20).
Figure Arizona.19
Figu
na.1
A high-angle
gle normal
n
fault is exposed along
Kingman. Above and below the
Interstate 40 several miles westt of K
marker bed are volcanic tuffs that are about 18 million years old.
Volcanic
anic activity
a
is evident in all sections of Arizona
with a co
combination of lava flows, cinder cones, and
stratovolcanoes.
ratov
A
Active volcanism spanned more than 15 million years
for the entire region.
Arizona.7
Formation of the Grand Canyon
No geologic feature is better known in Arizona than the
Grand Canyon. Located on the southwestern edge of the
Colorado Plateau, the canyon is famous throughout
the world for its beauty and grandeur, which is the result of
the Colorado River cutting through several thousand feet
of the sedimentary and metamorphic rocks. We have previously described the stratigraphic units that are found in the
canyon (Figure Arizona.21). We will now look at the
processes that contributed to its actual formation. Much
debate has existed about the ancestral history of the
Colorado River, but current thought is that the early stages
of the river flowed along the present path of the river in the
eastern portions of the canyon and then turned to the
northwest near the Kaibab Plateau. Following the opening
of the Gulf of California in the Late Miocene, that drainage
was captured by headward erosion of the lower Colorado
River. The time frame for the total development of the
Colorado River is estimated at about 6 million years.
During the erosion of the canyon, a process that is active
today, massive amounts of sediment have been transported
downstream for eventual deposition in the Gulf of Mexico.
Prior to the construction of a series of dams on the river,
Arizona
Geology of Arizona
Figure Arizona.21 Grand Canyon stratigraphic column showing
rock units found in the canyon.
Source: Web page of R. C. Blakey. http://jan.ucc.nau.edu/~rcb7
including the Glen Canyon Dam and Hoover Dam, periodic
floods served to clean out accumulated sediment and to
keep the river path clear of vegetation. Beaches were built
naturally by the deposition of sand and silt (Figure
Arizona.22). Damming of the river has greatly reduced the
amount of sediment, as it now collects behind the dams and
upsets the overall ecosystem of the river and the canyon.
Recent research has shown that periodic major water
releases from the dams, particularly from Glen Canyon
Dam near Page, Arizona, can be beneficial to the buildup of
beaches along the river and help restore some of the
ditions that have struggled
wildlife and other biological conditions
ars since Glen Canyon Dam
mw
to exist over the past 45 years
was
n 1
dedicated in 1966. It began impound
impounding water in
1963
(Figure Arizona.23).
o ey
Several features make the Grand Canyon so
eye-appealing
iew it. The exposed sedimentary
ment
to those who view
rocks distha stand outt ag
play a range of colors that
against a normally
one who has seen the
bright, clear blue sky. F
For someone
ral dozen times, thee var
canyon se
several
various combinations of
rent lighting
lightin and weather cond
different
conditions produce views that
aree distinct from others onee mig
might have seen. A combination
Figure
gure Arizona.23
A
Glen Canyon Dam on the Colorado River,
northern
nor
rn Arizona.
Figure Arizona.22 Sandbar beach along the Colorado River at
Mile 119 in the Grand Canyon. Arrows display the movement of water.
Note how an eddy is created behind the point bar along the left side
of the river.
Photo courtesy of Glen Canyon Monitoring and Research Center, USGS.
Courtesy of the Bureau of Reclamation.
12
Arizona.9 Water Resources
of magnificent cliffs separated by slopes of varying widths
produce a variegated series of surface that absorb and
reflect light in many different ways.
Although there are deeper canyons on Earth (such as
Hells Canyon in Idaho), Grand Canyon has several unique
attributes that have gained it fame. Standing on one rim, a
person can easily see the other side, which ranges in distance from 3 kilometers to close to 30 kilometers away.
Section Arizona.7 Summary
Grand Canyon is cut into the Paleozoic sedimentary
rocks on the Colorado Plateau and has its foundation in
Proterozoic rocks exposed along the Colorado River.
Construction of dams along the Colorado River have
affected the movement of sediment downstream and
have altered the ecosystems found in the canyon.
Arizona.8
Economic Resources
Geology has played a key role in the development
elopmen and
nd
expansion of the state. Primarily known for its cop
copper
d gold, sil
mines to the south, Arizona has also produced
silver,
uranium, precious stones, and even a small amo
amount of oil
arly
over its more than 1,000 years of inhabited histo
history. Early
uring the
discoveries of turquoise by Native Americ
Americans during
urce of ba
ter fo
first millennium became a source
barter
for their interacn the region
tion with other groups in
region. In the early 1500s
ed of areas tha
ed gold and
Spanish explorers learned
that contained
ir pursuits tturned up
p nothing and
silver deposits, but their
they returned to Spai
Spain empty h
handed. Almos
Almost 300 years
re was a resurgence off inter
passed before there
interest to look for
ars o
valuable minerals. Withi
Within 30 years
of the Gadsden
Purchase in 1854, a mo
move that brou
brought portions of the
west into th
Southwest
the United State
States, the railroad finally
ched the state.
ate. W
able, long-range transportation
reached
With reliable,
n place, silver and copper,
er, w
in
which had been discovered in
the southern portion, became
ecam a viable asset.
pan
Sincee th
the early Spanish
explorers visited the American
ir u
Southwest in their
unsuccessful search of gold and silver,
the region has rend
rendered a range of minerals that have made
ade in ore production. By far the greatest minthe state a leader
eral resource has been copper, which passed gold and silver
more than 125 years ago in terms of its dollar production.
Today the price of copper has risen to new record highs,
spurring the introduction of new mines in the state and
causing a resurgence in activity in existing mines.
Arizona has ranked among the leading states in the production of uranium, with the majority of ore being mined
on the Colorado Plateau. Although the late 1980s saw a
decrease in production, there has been renewed interest in
starting production of some older mines as the need for
uranium for nuclear power plants has increased. Much of
the ore is found in collapse features that exist in the
13
Mississippian Redwall Limestone in northern Arizona.
Sedimentary units in the Mesozoic rocks of the Colorado
Plateau also serve as sources for uranium oxide, including
the Chinle Formation.
Northern Arizona is the site for one of the largest coal
mining operations in the country. The region around Black
Mesa on the Navajo Reservation contains massive reserves
of coal, which is found in Late Cretaceous rocks. A combination of surface and underground mining is used to extract
the coal, which is shipped to power plants in the region.
Much of the coal is move
moved by slurry systems that use a large
water tak
amount of groundwater
taken from the Navajo Sandstone,
q
the regional aquifer.
ineral resources exist within
hin
n th
Other mineral
the state. Arizona
al g
has a small amount of oil and natural
gas. Its deposits are
d in the far nor
located
northeastern corn
corner of the state. In addin there are several hundred
red operations throughout the
tion
tate that extra
state
extract industriall min
minerals such as sand and gravel,
along with a wide range
ange of minerals including potash,
feldspars, b
d cem
barite, and
cement.
Section Arizona.8
S
Arizo
Summary
The mineral
min
resources of Arizona are wide ranging,
copp is the primary material that is mined.
but copper
Co
Coal is extracted on the Navajo Reservation and used
to power the Navajo Generating Station north of Page,
Arizona.
Arizona.9
Water Resources
Most of Arizona lies in a desert setting, an area that is
defined as receiving less than 25 centimeters (10 inches) of
annual rainfall (Figure Arizona.24). The average rainfall for
Phoenix is 7.5 inches per year and that of Tucson is 11.4
inches per year. With the rapid rate of population growth
since 1980, the state has been challenged to provide sufficient water. This problem has become more acute since the
mid-1990s, when the American Southwest saw the onset of
a drought that is approaching 20 years’ duration. People
still move to the region, and water conservation is slow to
take place. Without insightful planning there will be major
problems in the coming years.
Water in Arizona comes from a variety of sources: reservoirs (large, 500 acre-feet; small, 15 to 500 acre-feet);
springs; groundwater related to aquifers; and the Central
Arizona Project. All these sources are affected by the overall
paucity of moisture as well as a very high evaporation rate
that removes a great deal of surface water and precipitation
as it falls to the ground. Southern and southwestern
Arizona have evaporation rates that exceed the precipitation
rates by as much as 15 times! Small streams exist at higher
elevations, but their flows are very low volume (Figure
Arizona.25).
14
Arizona
Geology of Arizona
In order for the state to grow, its early settlers saw the
need to get water to the cities. The obvious source was
the Colorado River, so plans were put into place to tap the
river. Congress authorized the Central Arizona Project
(CAP) in 1968, but construction did not begin until 1973.
The first delivery of water occurred in 1985, and the 336-mile
(541-kilometers) long aqueduct was deemed completed in
1993. The CAP can deliver up to 1.5 million acre-feet of
water. Water is taken out of the river near Lake Havasu
City and channeled across the desert, through Phoenix,
until the canal terminates on th
the San Xavier Indian
Reservation, southwest of Tucson.
Water must be lifted as
on. Wat
much as 880 meters (2,900
mountains before
0 feet) over mo
ore it
begins its gravity flow across
significross the state. However, a sign
cant amount of this waterr evapor
evaporates as it travels across
acro the
arid desert.
Figure Arizona.24 Deserts in Arizona have minimal vegetation,
occasional cactus, and a pavement devoid of soil.
Section Arizona.9 Summary
S
ry
Arizon
Arizona’s growing
growin population
tion has substantial water
eeds because the majorityy of tthe people reside in desert
needs
c
or semi-arid conditions.
Figure Arizona.25 Streams such as Oak Creek near Sedona are
rather rare in the state. This perennial stream flows into the Verde
River, which eventually connects with the Salt River near Phoenix.
The CA
CAP provides
des a significant amount of water to
citi s an
cities
and farms in the southern part of the state.
Photo by W. Sylvester Allred.
Arizona
Arizona.10
Environmental Concerns
Envir
and Geologic Hazards
Arizona is situated in a semi-arid, temperate climate region.
Annual rainfall ranges from less than 10 centimeters
(4 inches) in many of the deserts to more than 70 centimeters (25 inches) in the higher elevations of east-central and
northern Arizona. Most of the precipitation falls during the
summer months when thunderstorms are common and
during the winter when weather systems bring snow to the
higher areas.
Due to the general lack of moisture in Arizona, there are
relatively few streams to move water across the surface.
Flooding does occur regularly due to copious, sometimes
torrential, rains that suddenly create surface flow that
is channeled into streams (Figure Arizona.26). Flooding is
common in the urban areas of Phoenix and Tucson because
much of the land area is covered by asphalt and other nonpermeable materials that prevent water from infiltrating
into the subsurface. Each summer portions of these two
metropolitan areas are flooded by sudden, torrential rains
that tax the capability of drainage systems to remove the
water.
In December 1978 heavy rainfall fell on an established
snow pack in the higher elevations. The resulting melting
produced record runoff and stream flows in rivers in the
Arizona.10 Environmental Concerns and Geologic Hazards
Figure Arizona.26 Bank erosion during flooding in southern
Arizona along the Santa Cruz River east of Nogales.
southern part of the state. Enough water flowed in
n the
Agua Fria River near the town of Black Canyon City to
ple died
destroy two bridges over Interstate 17. Several peo
people
he same storm
rm
as they drove off the highway in the night. The
h had the eerocreated massive flows in the Salt River, which
unway at S
sive power to remove hundreds of feet of runway
Sky
nix.
Harbor International Airport in Phoenix.
ea saw even lar
ow
Within two years the Phoenix area
larger flows
ar period
in the Lower Salt River. This was part of a 5-year
edly w
nhanced
that brought large flows thatt undoub
undoubtedly
were enhanced
ed surface
by increased population growth an
and increased
king lots, building
buil
runoff due to more parking
roofs,, and other
er ground that
impermeable surfaces. These structu
structures cover
once could take in the moisture.
b regions produ
Sudden flows across u
urban
produce flash floods
over roadways that are generally
enera dry. Motorists
that often cover
hese washes, only to dissometimess try to drive tthrough these
em. Arizona has a Stupid
cover the
they cannot traverse them.
torist Law that n
ws res
Motorist
now allows
rescuers to fine drivers up to
$2,000 to be saved from their
heir fflooded vehicles.
lthough we do not tend to think of earthquakes affectAlthough
zon there have been some significant ones that
ing Arizona,
have occurred in or n
near the state. The Arizona Geological
orte that more than 20 events of magnitude
Survey has reported
hav affected different areas of the state since
5 or greater have
1850. Two of the largest, the Sonoran earthquake (M 7.4)
of 1887 and the Imperial Valley, California, event of 1940
(M 7.1) produced significant damage in southern Arizona.
In 1912 there was an earthquake near Flagstaff that measured M 6. This event was felt over a wide area and produced some structural damage to homes in the region.
The area most likely to sustain earthquake activity is in
the northern and extreme southwestern portions of the
state (Figure Arizona.27). The Intermontane Seismic Belt
stretches from Montana through Utah and into northern
Arizona, where it passes just south and west of portions of
the Grand Canyon. Seismic activity has also been recorded
Figure Arizona.27 Earthquake hazard map.
Map courtesy of the Arizona
A
Geological Survey.
Photo courtesy of John Hays, Santa Cruz County Flood Control District, Arizona.
15
just north of Flagstaff as recently as 1993. Northern
A
Arizona is criss-crossed by many different faults. Although
not termed active, they do have the ability to move if the
stresses accumulated beyond the ability of the underlying
rock to quietly accommodate them. Earthquake activity in
the far southwestern corner of Arizona is related to the San
Andreas fault system, which is located in southeastern
California. Yuma is clearly at risk from this possible seismic
activity.
Land Subsidence and Expansive Soils
Aridity has produced large areas within the state where the
upper soil surface is very dry. During the past century
groundwater levels have dropped by several hundred feet in
portions of south-central Arizona. These water level
changes cause ground subsidence, as water in the subsurface
produces a buoyant effect on overlying material. Once this
process takes place, it is not possible to raise the surface
back it its original level.
Section Arizona.10 Summary
Flooding is the primary geologic hazard, as a combi-
nation of summer monsoonal thunderstorms and late
winter snowmelts increase stream and surface flow.
Arizona is relatively safe from earthquakes, although
portions of the state have been affected by more than
20 M 5 events over the past 150 years.
16
Arizona
Geology of Arizona
Review Workbook
ESSENTIAL QUESTIONS SUMMARY
Arizona.1 Introduction
What role has plate tectonics played in creating Arizona’s landscape?
When continental lithosphere collided and added new terrane to
existing landmasses, metamorphic and igneous rocks were
formed, many of which are now mountain ranges. There were
also periods of active subduction that generated both extrusive
and intrusive rocks that created other mountains and individual
peaks within the state.
What are the three physiographic provinces found in Arizona?
From north to south, the three provinces are the Colorado
Plateau, the Transition Zone, and the Basin and Range Province.
Arizona.2 The Proterozoic Foundation of Arizona
What primary process was involved in forming the land in Arizona’s
early history?
Plate collisions accreted landmasses to each other with the end
result being a larger continental mass that had relatively distinct
blocks of different ages.
Where do we see Proterozoic rocks exposed in the state today?
st
Proterozoic rocks are common in a line extending from northwest
Arizona to the southeast region, with significant outcrops also
occurring in the southwest portion of the state.
Arizona.3 Paleozoic Clastics and Carbonates
transgressions
sions and
What evidence do we have that several episodes of transgre
regressions deposited thick sedimentary sequences?
Throughout the state we find a mixture of sedimentary ro
rocks
associated with continental and shallow water marine de
depositional
itions. We see an alternaaenvironments, in addition to desert conditions.
ocks, aalong
ong with ch
etion of coarse- and fine-grained rocks,
chemical precipitates, that point to a change in the envi
environments under which
these rocks formed.
inundations that covered
red A
Arizona?
How extensive were the marine inu
rea aalong the
With the exception of the DefianceDefiance-Zuni uplift area
na–N Mexico
xico b
llowpresent-day Arizona–New
border, shallow-water
marine
und throug
hickn
deposits are found
throughout the state. Thicknesses
range from
an 400 meters.
0 to more than
Arizona.4 Transitions during the
eM
Mesozoic Era
Why were there extensive sand and rriver deposits covering the northeastern portion of the state?
A well-developed system off riv
rivers drained the continent and
deposited mudstones and sandstones over a wide area.
Where were the sources for volcanic deposits in southern Arizona?
During the Jurassic Period subduction of the eastward-moving
Pacific Plate produced volcanoes that extruded lava and pyroclastic debris onto the continent.
Arizona.5 Laramide and Mid-Tertiary Upheaval
What role did plate tectonics play in creating geologic features in
Arizona?
These orogenic events produced numerous intrusive bodies that
eventually were exposed when the overlying country rock was
removed through erosion. Tectonic forces associated with the
mountain building also generated faults and movement in the
crust that produced many monocline in north-central Arizona,
especially around the Grand Canyon region.
Arizona.6 Volcanic Activity
What are the time span and spatial extent of volcanism?
Volcanism during the Jurassic Period pro
produced extrusive features
owing th
in southern Arizona. In a period following
the mid-Tertiary
od
orogeny 30 million years ago, there wass a 15-mi
15-million-year period
that saw many volcanic fields form in central an
and southern Arizon
Arizona.
ral million years has created oth
er
Activity during the past several
other
orthern aand southwestern
nA
peaks and volcanic fields in northern
Arizona.
canic features have
ve been formed?
What types of volcanic
va fields there are cinder cones,
es, sstratovolcanoes,
In addition to lava
and domes.
Arizona.7
.7 Formation
rmation o
of the Grand
nd C
Canyon
Colorado River form
m the Grand Canyon?
How did the Co
eexisting drainage
drain
ern A
Preexisting
in northern
Arizona that flowed from east to
est and then n
west
northward was ca
captured by a river that extended its
le
ngth as the Gulf of California
aliforn began to open. Once this river
length
was able
le to lengthen itself deeper onto the continent, it cut off the
ancien
ancient drainage pattern and formed the Colorado River that
ow to the south.
outh.
flowed
ere did all tthe eroded material go?
Where
Thousands of cubic kilometers of surface rocks were moved
downstream and deposited into the Gulf of California. Obviously
this was lon
long before the building of dams along the Colorado
River, whic
which now impede sediment flow.
How dynamic is the Grand Canyon in terms of changing in the future?
H
Geologic processes are continually are work in the canyon and
there is always change taking place. The presence of dams
along the Colorado River now prevent sediment from being
moved to the mouth of the Colorado River in Mexico.
Arizona.8 Economic Resources
Why is Arizona home to some of the largest copper deposits in the
world and how have they contributed to the development of the state?
Many of the rich copper deposits are associated with the massive
intrusive plutons formed during the Laramide Orogeny. Copper
has been the mainstay of the mining industry in Arizona since the
late nineteenth century and has recently seen a resurgence due to
higher prices.
What does the future hold for mining in the state?
Mining will continue to play an important role in the economy of
the state. The existence of large copper and coal deposits will
continue to generate jobs and serve as bases for providing much
needed natural resources for the nation.
Arizona.9 Water Resources
Where does Arizona get its water?
Although Arizona lies in desert and semi-arid climates, it does
have some impounded surface water and groundwater available
for human use. A significant amount of water for the major metropolitan areas of Phoenix and Tucson is taken from the Colorado
River by the Central Arizona Project.
Review Workbook
What is the future of water in Arizona?
The availability of adequate water supplies will dictate the future
development of the state. Unless new sources are found, it will be
a challenge to growth in a region that is attracting more people
each year.
Arizona.10 Environmental Concerns and Geologic Hazards
Has Arizona experienced natural disasters in the past?
Arizona has experienced earthquakes in the past century, with
17
most of the relatively small events occurring in the northern and
far southwestern areas. The most likely disasters are floods, which
are produced by heavy seasonal rains that quickly fill stream
channels and affect newly populated areas.
How stable is the state in terms of future disasters?
Predicting future events of any type is difficult, but Arizona is
fairly safe from volcanic eruptions and earthquakes. Flooding is
the greatest threat to the state, along with long-term drought.
ESSENTIAL TERMS TO KNOW
Accretion the process of adding crustal rock that originated
Lithosphere Earth’s outer, rigi
rigid part consisting
sting of the upper
elsewhere to another large block of continental material.
mantle, oceanic
crust.
nic crust and continental
cont
t.
Basal at the bottom of a sequence.
Ma megaannum;
aannum; 1 mill
million years ago.
Basalt an iron- and magnesium-rich extrusive rock that is
Metasedimentary
etasediment
a term applied
lied to sedimentary rocks that
have
to metamorphic
processes.
ave been subjected
subjec
morp
relatively low in silica. Basalt lava is very fluid, displaying low
viscosity.
Metavolcanic a term applied
Metavolcani
pplie to volcanic rocks that have been
Basement rock that rests on the bottom of a sequence; see basal..
metamorph
metamorphosed.
Basin and Range Province a physiographic region of thee
in
western United States characterized by alternating mountain
ranges and valleys.
Orogeny the process
Or
ocess of forming mountains, especially by
Colorado Plateau a physiographic region of the western
ic past.
pas
geologic
United States characterized by relatively horizontall sedimentar
sedimentary
eous intru
layers along with mountains that formed due to igneous
intrucanic material
sions and a lesser amount of extrusive volcanic
material.
Physiographic
hysio
region an area that has similar structures that
devel
developed
by similar tectonic or geomorphic processes.
Craton the relatively stable part of a continent;
ontinent; consists of a
ension o
ncient
shield and a platform, a buried extension
off a shiel
shield; the ancient
nucleus of a continent.
fol
rust faulting.
f
folding
and thrust
Paleotopography
pogra
the surface topography of a region in the
Pluton an igneous intrusion formed when rising magma cools
P
and crystallizes below the surface.
Quartz arenite a sedimentary rock consisting of a high
Deformation any change in shape or vol
volume, or both,
th, of rocks
percentage of quartz in sand-size fragments.
rmation involv
in response to stress. Deformation
involves folding and fractu
fracturing.
Regression a retreat of the sea from adjacent land.
Disconformity an
n uncon
unconformity
formity tha
that is bounded
ed by parallel layers.
Roof pendant a projection of an overlying rock unit into an
igneous intrusion.
Eolian related to thee effect oof a wind-controlled
rolled environment.
Epicontinental
nental located oon the continental
nenta shelf or interior edge
ont nent.
of the continent.
Fluvial
uvial related too st
stream or river
er en
environments.
Ga gigaannu
gigaannum; 1 billion years
ears ago.
Granodiorite
dio
a coarse-grained
se-g
plutonic rock of intermediate
composition.
Karst topography
raph a surface containing caves, sinkholes, and
ys that is produced by active chemical erosion and
solution valleys
collapse of an underlying limestone layer.
Spheroidal weathering a type of weathering in which corners
and sharp edges of rocks weather more rapidly than flat surfaces,
thus yielding spherical shapes.
Subduction zone an area where one lithospheric plate
descends beneath a second plate.
Time-equivalent term applied to geologic units that formed at
the same time but in different locations.
Transgression the covering of land areas by the sea.
Unconformity a break in the geologic record represented by an
erosion surface separating younger strata from older rocks.
Laramide Orogeny a period of extensive tectonic activity that
affected the western United States from about 80 Ma to 55 Ma.
MORE ON ARIZONA GEOLOGY
Below are some suggestions on ways to explore the geology of
Arizona:
The single best source for information about the geology of
Arizona is the Arizona Geological Survey, which has its main
office in Tucson with a branch in Phoenix. The survey sells guidebooks, maps, and many scientific publications that address a wide
range of topics about the subject. The survey is found online at
http://www.azgs.state.az.us/.
18
Arizona
Geology of Arizona
Other excellent sources include the U.S. Geological Survey,
which has Web sites for each state. Go online at
http://www/usgs.gov/state and select Arizona (or any other state
of interest). For specific information on water and hydrology for
Arizona, go to http://az.water.usgs.gov/.
Two sites that are maintained by university professors include the
one belonging to Dr. Stephen Reynolds at Arizona State
University. At his site, http://reynolds.asu.edu/home.htm, you can
access information on the state, including many three-dimensional
representations of geologic settings. An excellent site for geologic
information depicting Arizona in the geologic past is found at the
site maintained by Dr. Ronald Blakey at Northern Arizona
University. His site is found through the departmental site at
http://www4.nau.edu.geology/. Then bring up his personal web
page.
Obviously the best way to see the geology of Arizona is to get out
and see it. Visit the numerous state and national parks, because
they are located in areas with superb exposures that are seen in
many photographs.
Think of geology as a subject that you can always use no matter
where you are on Earth. Take more courses so you can develop a
solid understand and appreciation of the processes that affect our
daily lives in often subtle ways. If you are at a community college
or university, look in the course catalog for courses that appeal to
you. Visit the geology or earth science department to learn more
about the opportunities they have to offer. As your interest grows,
consider becoming a student member of the Geological Society of
America. More information is available online at
http://www.geosociety.org.
Whenever you travel in Arizona, there are several excellent books
that can serve as sources for more information. Geology of Arizona,
written by Dale Nations and Edmund St
Stump and published by
Kendall/Hunt Publishing Company, Dubuq
Dubuque, Iowa, provides
n in Ariz
details about many of the features seen
Arizona. For more
noes in northern A
endell
specific information on volcanoes
Arizona, Wendell
ern Arizona, published
bl
G
Duffield’s Volcanoes of Northern
by thee Gra
Grand
cellent re
os who
h like
Canyon Association, is an excellent
resource. For those
a s Hiking Arizona
to hike, Ivo Lucchitta’s
Arizona’s Geology, publ
published by
rs Books, Seat
n, is a very useful
The Mountaineers
Seattle, Washington,
gy in specific pa
te. T
source of geology
parts of the state.
The Geologic
Highway Map of Ar
Arizona, avai
available from the A
Arizona Geological
nderful reso
u driv
Survey, iss a wonderful
resource as you
drive across the state. Most
se ite
re availa
of these
items are
available at state and national park bookstores.