A canyon is a deep valley between cliffs often carved from the landscape by a river. Most canyons were formed by a process of long-time erosion from a plateau level. The cliffs form because harder rock strata that are resistant to erosion and weathering remain exposed on the valley walls. Canyons are much more common in arid areas than in wetter areas because weathering has a greater effect in arid zones. Canyon walls are often formed of resistant sandstones or granite. Great place to hide if your a wanted man.