Double Arch is a close-set pair of natural arches in Arches National Park in southern Grand County, Utah, United States, that is one of the better known features of the park. Double Arch was formed differently from most of the arches in the park. It is what is known as a pothole arch, formed by water erosion from above rather than more typical erosion from the si…Double Arch is a close-set pair of natural arches in Arches National Park in southern Grand County, Utah, United States, that is one of the better known features of the park. Double Arch was formed differently from most of the arches in the park. It is what is known as a pothole arch, formed by water erosion from above rather than more typical erosion from the side. The larger opening has a span of 148 feet and a height of 104 feet. These dimensions give the arch the tallest opening and second-longest span in the park.