NPS said it was formed from 190 million-year-old Navajo sandstone, which originated in the late Triassic to early Jurassic period. The weather slowly eroded the fine-grained sand feature.

The National Park Service said the arch was formed from Navajo sandstone that originated in the late Triassic to early Jurassic periods. Since it was formed, the NPS said the arch “has been ...