Arches National Park

May 31, 2014

As its name proclaims, Arches National Park contains a remarkable number of natural rock arches, as well as a rich variety of other sandstone wonders. The NPS brochure describes its origins this way:
Arches National Park
The park lies atop an underground salt bed that is responsible for the arches, spires, balanced rocks, sandstone fins, and eroded monoliths [...]. Thousands of feet thick in places, this salt bed was deposited across the Colorado Plateau 300 million years ago when a sea flowed into the region and eventually evaporated. Over millions of years, residue from floods, winds, and the oceans that came and went blanketed the salt bed. The debris was compressed as rock, at one time possibly a mile thick.

Salt under pressure is unstable, and the salt bed lying below Arches was no match for the weight of this thick cover of rock. The salt layer shifted, buckled, liquefied, and repositioned itself, thrusting the rock layers upward as domes, and whole sections fell into the cavities [left when the salt moved].

Faults deep in the Earth made the surface even more unstable. [...] Fault-caused vertical cracks later contributed to the development of arches. As the salt’s subsurface shifting shaped the Earth, surface erosion stripped off younger rock layers. Except for isolated remnants, today’s major formations are salmon-colored Entrada Sandstone, in which most arches form, and buff-colored Navajo Sandstone. They stand like a layer cake over most of the park. Over time water seeped into superficial cracks, joints, and folds. Ice formed in the fissures, expanding and pressuring the rock, breaking off bits and pieces. Wind later cleaned out the loose particles, leaving a series of free-standing fins. Wind and water then attacked these fins until the cementing material in some gave way and chunks of rock tumbled out. Many of these damaged fins collapsed. Others, hard enough and balanced, survived despite missing sections. These became the famous arches. Pothole arches are formed by chemical weathering as water collects in natural depressions and then eventually cuts through to the geologic layer below. This is the geologic story of Arches National Park—probably. The evidence is largely circumstantial.
The NPS website about Arches includes an animated video that presents this information more vividly, if you’re interested. In the menu on the left side of that NPS homepage (under the heading “Explore This Park,” click Photos and Multimedia, then Multimedia Presentations, then Geology of Arches. You can even download your very own copy.
Moab and nearby parks
The map at the left shows the three parks we visited and the town of Moab, where we stayed. It takes in a wide area so that you can see how the Green River comes down from the north and joins the Colorado inside Canyonlands, which the rivers divide into three sections.

If you click the map, you’ll see just a part of it expanded—the part that shows the routes we took from Moab to get to each of the parks. It shows where we entered each park, but not where we went once we were inside. The expanded version doesn’t give you the full overview, but at least the labels on the map are big enough to read.

As the map shows, the entrance to the Arches National Park is just a few miles north of Moab. We followed guidebook advice to get there early in the morning—kind of early, anyway. There were plenty of other visitors, but not so many as to interfere seriously with our picture-taking. The map in the NPS brochure would probably have served us very well, but in Moab we had bought a more detailed National Geographic map of the park, so we followed that, going everywhere that we could drive.
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Colorado National Monument
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Colorado River Valley
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Arches National Park
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Dead Horse Point State Park
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Canyonlands National Park
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Lake Powell Boat Trip
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Canyon de Chelly, Inside
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Canyon de Chelly, North Rim
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Canyon de Chelly, South Rim
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Cumbres & Toltec Scenic Railroad
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Garden of the Gods
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Faces
Site Map
Home
    Navigation and Display
    Where We Went

Colorado National Monument
    Gallery       Notes

Colorado River Valley
    Gallery       Notes

Arches National Park
    Gallery       Notes

Dead Horse Point State Park
    Gallery       Notes

Canyonlands National Park
    Gallery       Notes

Lake Powell Boat Trip
    Gallery       Notes

Canyon de Chelly, Inside
    Gallery       Notes

Canyon de Chelly, North Rim
    Gallery       Notes

Canyon de Chelly, South Rim
    Gallery       Notes

Cumbres & Toltec Scenic Railroad
    Gallery       Notes

Garden of the Gods
    Gallery       Notes

Faces