How are Arches Formed?

The Slow Formation of an Arch

Underneath Arches National Park lies a salt bed layer, which was deposited some 300 million years ago when the area was part of an inland sea. When the sea evaporated, it left salt deposits; some areas collected over a thousand feet of these deposits. During the next millions of years, the area was filled with debris deposited from winds, floods, streams and oceans that came and went. Over time this debris compressed into rock. The weight of the rock layer caused the salt bed below to become fluid, allowing it to thrust up and create domes and ridges.

What happened after the movement of salt molded the landscape? Erosion went to work on the surface rock layers and ground water began to dissolve the underlying salt deposits. Water seeped through cracks in the weathered rock and ice formed, further expanding the crevices and weakening the rock. Eventually, the domes began to collapse leaving a maze of vertical free-standing rock walls known as fins. Wind and water continued to assault these fins until they eventually wore through and pieces began to fall away, creating the amazing arches you see today.