Here's why:

* Running water is the key element. Canyons are formed by the erosive power of rivers over long periods.

* Erosion: The water cuts through the rock, gradually carving out a deep, narrow valley with steep sides.

* Examples: The Grand Canyon in Arizona, the Yarlung Tsangpo Grand Canyon in Tibet, and many others.

Let me know if you'd like to learn more about other landforms!