Double O Arch, Devils Garden Trail, Arches National Park, Moab, Utah, USA. Double O Arch is the second largest arch within the Devils Garden area. Its larger arch spans 71 feet, stacked atop a 21-foot arch on the same sandstone fin. Double O Arch is 1.93 miles from the Devils Garden trailhead at the far end of the Devils Garden Primitive Loop. This image was stitched from multiple overlapping photos.
A thick underground salt bed underlies the creation of the park's many arches, spires, balanced rocks, sandstone fins, and eroded monoliths. Some 300 million years ago, a sea flowed into the area and eventually evaporated to create the salt bed up to thousands of feet thick. Over millions of years, the salt bed was covered with debris eroded from the Uncompahgre Uplift to the northeast. During the Early Jurassic (about 210 million years ago) desert conditions deposited the vast Navajo Sandstone. On top of that, about 140 million years ago, the Entrada Sandstone was deposited from stream and windblown sediments. Later, over 5000 feet (1500 m) of younger sediments were deposited and then mostly worn away, leaving the park's arches eroded mostly within the Entrada formation. A thick underground salt bed underlies the creation of the park's many arches, spires, balanced rocks, sandstone fins, and eroded monoliths.