Standing on the rim, the drop looks almost vertical. A canyon is a deep, narrow valley with steep sides, usually carved by a river over long periods. The walls expose layers of rock that record ancient environments.

The Grand Canyon is the most famous, but similar features appear wherever rivers cut into uplifted plateaus. Flash floods can deepen canyons rapidly in arid climates. Width varies from slot canyons only meters across to vast chasms many kilometers wide.

Canyons create dramatic microclimates and isolated habitats. They also present engineering challenges for roads and pipelines. Hikers and geologists prize them for the clear view of Earth’s history written in stone. The river at the bottom continues its slow work of removal.

• Deep valley with steep sides
• Primarily formed by river erosion
• Exposes stratified rock layers
• Ranges from narrow slots to wide chasms