Double O Arch in Arches National Park near Moab, Utah, consists of two natural arches formed in the same fin of rock. Located in the Devils Garden area, it is the second-largest arch there after Landscape Arch. Its unusual appearance comes from two openings stacked vertically, with a larger upper span of 71 feet and a smaller lower opening about 21 feet across. Reached by a strenuous 4.1-mile round-trip hike on the Devils Garden Trail, it is both a striking geologic feature and a popular destination within the park.