Here's how it works:

* Water is the primary agent of erosion: Rivers and streams carve out canyons over long periods. The flowing water carries sediment and rocks, which wear away the bedrock.

* Gravity plays a role: As the river erodes downward, the canyon walls become steeper and more vulnerable to gravity. Rockfalls and landslides contribute to the canyon's deepening and widening.

* Other factors contribute: Wind, glaciers, and even tectonic activity can also play a role in canyon formation, though water erosion is the most common and powerful force.

Examples:

* The Grand Canyon: Formed by the Colorado River over millions of years.

* The Bryce Canyon: Formed by erosion of sandstone by frost wedging and other processes.

* The Canyonlands National Park: A complex landscape of canyons, mesas, and buttes formed by erosion of the Colorado Plateau.

Key takeaway: Canyons are a testament to the power of erosion and the slow but relentless force of nature over time.