How Are Arches Formed?

Natural arches form over millions of years. The process begins when sandstone layers crack and separate, then erode slowly through water, wind, and temperature changes. Even a small opening you see today has likely been thousands of years in the making.

Moab’s geology is unique. The area’s thick sandstone layers—especially the Entrada and Navajo formations—were cracked and lifted by ancient salt deposits below. Those fractures created ideal conditions for erosion to carve fins, then arches. No other place combines those exact ingredients on such a massive scale.

Yes! Other places like Canyonlands National Park and Bryce Canyon National Park also feature natural arches, though Arches NP has the highest concentration.

Yes, Arches is open year-round. However, some trails may be closed during winter due to snow or weather conditions.

You can hike several trails in Arches NP to get up close to the formations. For more detailed information, consider taking a guided tour that focuses on the geology of the park.

Most arches are carved from Entrada Sandstone, a soft, fine-grained rock formed from ancient desert dunes about 150 million years ago. Some are also found in Navajo Sandstone, which is slightly older and more resistant.

The same forces that create arches—water, wind, and gravity—also destroy them. As erosion continues, the arch thins until it can no longer support its own weight. When it collapses, it leaves behind rock spires or new formations that may one day start the process again.

An arch forms primarily through wind, frost, and erosion in sandstone fins. A natural bridge, like those found in Natural Bridges National Monument, forms when flowing water from a stream or river carves through rock. Same concept—different sculptor.

Yes! The cycle of formation and collapse is ongoing. New cracks are constantly opening in sandstone fins, and erosion is slowly shaping the next generation of arches right now.

Delicate Arch is the park’s most iconic formation. It began as part of a sandstone fin in Entrada Sandstone, where erosion widened an opening until the center fell away, leaving the graceful arch we see today.

Park geologists and researchers use laser scanning, drones, and 3D modeling to measure arch thickness and movement. These tools help predict when parts may collapse and document changes over time without disturbing the formations.