Download Geology - Escalante

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Maureen McDonald
Dean Cochran
4/6/13
Final Paper
Escalante State Park
After a twelve-day excursion to America’s Southwest and seeing many of the greatest
landscapes and geological formations that America has to offer my view of geology has been
dramatically changed for the better. After, being to all of these dramatically different areas I had
to come down to a decision on to what focus on. The State Park that struck me the most was
Escalante. Escalante was a very unique State Park because all of the diversity that it had to offer
within the 2,969 square miles of park located in southern Utah. The park also has a dramatic
elevation variation at Lake Powell the elevation is at 3,900 feet and goes to 9,280 feet at Canaan
Peak. In Escalante there is “more than 200 million years of geologic history revealed in
exceptionally well-exposed, mostly Mesozoic strata bent by a series of monoclines and anticlines
that clearly influence today’s topography (Lucy).” In this paper I will especially focus on two
different parts of Escalante that are really intriguing; these two are the Escalante Petrified Forest
State Park and Escalante Grand Staircase National Monument.
Escalante Petrified Forest State Park is a very unique part because of all of the deposits of
petrified wood. The petrified wood varies in size from an inch to some pieces as long as five feet.
The geological history of how the Petrified Forest came about is because it was once a bottom of
a flood plan; it now sits above on a mesa.
“Approximately 135 to 155 million years ago, trees up to 100 feet tall were uprooted and
buried in the mud during flood periods. Ground water permeated the buried trees over
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millions of years. Because of the oxygen-free environment, the trees did not decay.
Instead through a complex process, silica solution in the groundwater replaced organic
material in the tree, leaving the cell structure intact. Due to erosion, this fallen forest of
petrified trees is now exposed (Utah DNR).”
In the Escalante Petrified Forest State Park there are different predominant rock formations. One
of the most predominant rock formations is Entrada Sandstone, which is an Escalante Member.
The Entrada Sandstone was “formed approximately 153 million years ago during the middle to
late Jurassic period (Escalante).” “Entrada Sandstone was named in 1928 after the Entrada Point
in the northern part of the San Rafael Swell (What).” The Escalante State Park Resource
Management Report states that, the Entrada Sandstone is visible as the light gray to white dunelike formations at the base of the cliffs. Management Report also states that the geologic history
of the Park is interrupted by a significant period of erosion. Another prominent formation seen
within the park is the Morrison Formation. “The Morrison Formation, formed between 146
million years ago and 138 million years ago during the late Jurassic period. Within the Morrison
formation there are three members found in the park: the Tidwell, Salt Wash, and Brushy Basin
(Escalante).” The Escalante State Park Management Report states that the Tidwell Member was
created from river sediments and is located in the Park as the lower reddish portion of the red and
white cliffs. The second member of the Morrison Formation is the Salt Wash. “Braided streams
deposited the materials forming the Salt Wash Member seen as the lighter colored cliff portion
capping the Tidwell (Escalante).” The third and final member of the Morrison Formation is the
Brushy Basin Member. “The Brushy Basin Member is 170 feet thick locally and composed of
mudstones, conglomerates, and sandstones. This member is best viewed from on top of the cliffs
and it also contains fossilized bones of the late Jurassic dinosaurs and the petrified wood
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(Escalante).” Another interesting part of the Brushy Basin is that it “represents changing
environments as the braided streams of the Salt Wash Member were replaced by migrating river
and lake deposits (Escalante).”
The second part of the Park I will cover is the Grand Staircase-Escalante National
Monument. Grand Staircase-Escalante National Monument is broken down into three different
regions within the three regions are the following: “Grand Staircase Region, Kaipaowits Region
and the third is the Escalante Canyon Region (Utah DNR).” During the Paleozoic Era “Permian
limestone was at surface level and shows us that early in Permian time, sand and silt washed into
the region from mountains uplifts in the west and mingled with limestone deposited in a shallow,
fluctuating western era (Lucy).” “By mid-Permian time, this region again rose above sea level,
and no further sediments accumulated until well into the Mesozoic Era (Lucy).” Monoclines and
anticlines also define the Grand Staircase. Monoclines “may form as near-surface rocks drape
over deeply buried normal or reverse faults (Chronic).” Anticlines “are uparched folds in which
the layering slopes in opposite directions, away from a common central ridgeline called the fold
axis (Fillmore).” Both the monoclines and anticlines have visibly affected the southern region of
Utah’s landscape.
The Mesozoic Era had many different formations, which included the Triassic Moenkopi
Formation, Chinle Formation, Kayenta Formation, the Morrison Formation, and finally the
Dakota Formation. The Triassic Moenkopi Formation is “deep red siltstone, sandstone, and shale
that were deposited on a broad, westward-sloping costal plain; Precambrian rocks contributed to
iron-rich minerals that gave the rocks their color (Lucy).” The Chinle Formation “was deposited
by the time the land had risen and little higher, and was cut off from the sea to the west. Where
the old streams were there are fossils, and petrified logs (Lucy).” In addition there is the Wingate
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Sandstone, which “marked with the long diagonal striations that indicate its sand dune origin,
changes into the Moenave Formation, red, silty river and lake deposits much like the Triassic
rocks (Lucy).” Also in the Jurassic age there was the Kayenta Formation. The Kayenta
Formation “is a sandstone and siltstone layer which lies above the Wingate Sandstone. They
contain fossils, petrified wood, and bones of vertebrate animals (Lucy).” Atop the Kayenta
Formation the Navajo Sandstone sits above. “With the uniform, rounded grains and distinctive
cross-bedding, the Navajo is clearly another wind-deposited sandstone. It represents an ancient
desert, an arid, dune-covered expanse rivaling the present Sahara (Lucy).” The next formation is
the Morrison Formation, “which is the uppermost Jurassic rock that was deposited by slowmoving winding streams, with occasional input of volcanic ash or development of sand dunes
(Lucy).” “Its soft, fine, clayey layers and pastel green and purple hues, with layers of yellowish
sandstone – the colors are due to the nonoxidized iron minerals that suggest a marshy or swampy
environment (Lucy).” The final formation is the Dakota Formation. This formation is midCretaceous time and is a thin but widespread unit-developed as the sea reached across the
beveled surface of the Jurassic rocks (Lucy).” The last formation that is seen is in the Cenozoic
Era, which is the Claron Formation. This formation forms “the Pink Cliffs of Bryce Canyon and
the Aquarius Plateau were the lake and river deposits can be seen in the distance (Lucy).”
There are some very interesting landforms that make up the Grand Staircase-Escalante
National Monument like the “high cliffs and wide, gently sloping benches rising from south to
north (Lucy).”
“The Grand Staircase includes, in ascending order, the Chocolate Cliffs, the Vermilion
Cliffs, the White Cliffs, the Gray Cliffs, and rising north of the national monument, the
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Pink Cliff of Bryce Canyon. Between the “risers” and of the staircase, the benches or
“treads” represent more easily eroded rock layers (Lucy).”
Both the Escalante Petrified Forest State Park and the Grand Staircase-Escalante National
Monument were wonderful places to visit and learn more about their geological history and
background about. Being able to say that I stood on a 200 million year old log is one of a kind
and I will appreciate every second of this geological expedition that I went on. I really believe
that I have a much deeper appreciation for all the beautiful and sometimes overlooked State and
National Parks that are here in the United States.