Arches National Park Research Project
Stephanie Hitchcock
Geology 1010
November 17, 2014
Moab, Utah hosts a plethora of geologic landscapes; Canyonlands National Park, Dead Horse
Point State Park, the La Sal Mountains and, of course, Arches National Park. Arches National Park
has a long story of being visited by humans. From the ancestral Puebloan hunter/gatherers to early
historical settlers who boasted the area’s amazing views and unique formations. Then, there are the
modern recreationists who flock to the park every year. There is also the old Atlas Uranium Mine
and tailings pit which is just outside of the park itself. Human activity, however, is a small part of the
story. Plenty of geological processes are at work above and below the surface that make Moab and,
specifically, Arches National Park what it is today. The much studied Moab Fault lies just South
West of the Arches National Park boundary. Then, at center stage, are the formations themselves,
slowly and naturally carved by wind, rain and subsurface movement.
Not much evidence is left over in Arches National Park from prehistoric visitors other than
petroglyphs and Chert rock tools. There is no evidence that they stayed in the region long. It’s more
likely they visited seasonally, got what they needed from the land and moved on. Historical settlers,
however, decided it was worth sticking around. In the 1850s, Mormons attempted to settle the area
but were unsuccessful due to human conflicts. But in the later 1800s, farmers, ranchers and
prospectors were successful at establishing themselves permanently (Oswald, 2012). Although, many
people marveled at the beauty Arches offered one man is considered one of the firsts to “market” it.
Loren “Bish” Taylor took over the Moab newspaper when he was just 18 years old in 1911
and often he would write about the unique and beautiful rock wonderland that was just north of his
frontier town (Oswald, 2012). Eventually this would gain the area enough popularity to start the
campaign towards it becoming a National Park. On April 12, 1929 President Herbert Hoover signed
Proclamation No. 1875 saying the areas locally known as “Devil’s Garden” and the “Windows” were
to be known as Arches National Monument and to forever be protected (Hoover, 1929). The
boundaries have grown since then from just under 5,000 acres in 1929 to almost 80,000 acres today.
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The uranium history in Moab goes back to the early to mid-1900s when the government was
conducting many investigations into uranium-containing ore deposits. Most of the ore deposits in this
region are from the Chilean Formation (Chenoweth, 1975). The mine and tailings pit that was
located, the tailings pit is still there, in Moab (just outside of Arches) was the fifth largest in the
world until being closed in 1984. It also has the title of being one of the most highly polluting
uranium operations. The pile was not lined and pollutants were allowed to seep into the ground and
disperse themselves into the surrounding area, including the Colorado River. There was also
contaminated dust and radon gas that went uncontrolled for most of the time that the mine was in full
operation. Today, the site is being cleaned up (UMTRA) and the tails are being hauled to a site in
Colorado.
Inside the park you will find more than 500 arches and a large number of different rock
layers (ages). Though the rocks throughout Arches range in age from Pennsylvanian (Paradox
Formation) to Cretaceous (Mancos Shale), the different Jurassic formations are by far the most
prominent (Foos, 1999). Two of the most prominent units are the Entrada Sandstone and the Navajo
Sandstone. The Entrada Sandstone is divided into three units: Moab Tongue, Slick Rock and Dewey
Bridge (Foos, 1999). The Slick Rock is probably the layer that is most well-known to non-geologists.
It is in the Slick Rock member that a good number of the Arches occur. The Slick Rock is a large
layer made up of reddish-brown Sandstone and is fairly friable. It also has the black markings of
desert varnish in the areas where it has formed cliffs. The Slick Rock member was deposited in a
dune environment by way of streams and wind (Foos, 1999). The Navajo Sandstone, also Jurassic, is
identified as typically being tan to light grey in color and is cross-bedded (Johnson and Thordarson,
1966). The Navajo lies under the Slick Rock when looking at a cross section. The cross-bedding
pattern indicates it was deposited by wind. One can easily find it in an area known as the “frozen
dunes” (Foos, 1999).
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Many formations have formed through water and wind deposition. At Arches National Park
subsurface movements of salt beds have shaped some of the landscapes. These salt beds are the
remnants of an enormous ancient sea that covered most of Utah. A cyclical series of flooding and
evaporation eventually left thousands of feet of salt, which sediments could then be deposited on to
(McCalla, 2008). Because of the low density of the salt and the relatively high density of the lithified
sediments some of the overlying rocks buckled the salt layers, which in turn caused other rocks to
thrust upward, exposing previously protected layers to weathering. These differences in density also
caused formations known as salt diapirs (Foos, 1999). It is because of the fragility of the salt beds
and through the weathering processes of wind, rain and frost wedging that the arches and large fan
formations were created.
Another smaller source of movement in the area is the Moab Fault. The Moab fault has three
sections and is one of the longest Cenozoic normal faults in the Paradox Basin (Olig, 1996). The
Moab fault is not a very active fault line. The evidence that is available tells us that the last
movement that was seen on the fault was 1.2 to 7.5 Ma and that any movement was most likely
tectonic and occurred before the Quaternary salt-dissolution subsidence (Olig, 1996).
Arches National Park is a very busy location. Human interaction is at an all-time high in and
around the park. The Earth is forever restless and the geologic processes are hard at work, constantly
shaping the landscape. You may not be able to see it but it is there. With every rainy or windy day a
little bit more of the friable Entrada Sandstone gets washed away. As well man made changes
through mining and recreation. In a few million years there will be a whole new family of arches,
cliffs and balancing rocks for future populations to enjoy.
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References
Chenoweth, W. L. (1975). Uranium deposits of the Canyonlands area. Canyonlands country,
eighth field conference.
Hoover, H. (1929). Arches national monument, a proclamation.
Foos, A. (1999). Geology of the moab region, arches, dead horse point and canyonlands.
Johnson, H. S., Thordarson, W. (1966). Uranium deposits of the moab, monticello, white canyon
and monument valley districts utah and arizona.
McCalla, C. (2008). Utah geological survey. The onion creek salt diaper, grand county.
Oswald, D. (2012). The moab canyons experience. The human history of arches national park.
Pages 7-11.
Olig, S. S., Fenton, C. H., McCleary, J., & Wong, I. G. (1996). The earthquake potential of the
Moab Fault and its relation to salt tectonics in the Paradox Basin, Utah.
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Figure 1 Formations near the entrance of Arches National Park
Figure 2 Formations with waterfalls from rain water near the entrance of Arches National Park
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Figure 3 Balanced Rock
Figure 4 Wide view of The Windows area with Turret Arch and an unknown Arch
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Figure 5 Double Arch
Figure 6 Formations and Arch near Turret Arch, Elephant Arch and Double Arch
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