The Petrified Dunes are a series of rock formations located in Arches National Park. It is aptly described as a geological wonderland. Set in the high desert of southeastern Utah, it is home to the largest concentration of sandstone arches in the world, some 2,000 in all. The dunes can be found just off of the park road between the Courthouse Towers and the Windows Area. The formation was produced when ancient sand dunes hardened into stone under the overlying subsequent material, which later eroded away. Over 100 million years of erosion created this awe-inspiring landscape. Over 100 million years of erosion created this awe-inspiring landscape. These sandstone arches and monoliths are transitory, occupying a millisecond on the clock of geological time.