Canyon
Grand Canyon, Arizona
A canyon, or gorge, is a valley walled by cliffs. Most canyons originate by a process of long-time erosion from a plateau level, with a stream gradually carving out its valley. 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 lesser effect in arid zones. Canyons' walls are often formed of resistant sandstones or granite.
The word canyon is Spanish in origin; in some parts of the United States, canyons are sometimes called gorges (the British English word) or notches.
In the southwestern United States, canyons are important archeologically because of the many cliff-dwellings built there, largely by the Ancient Pueblo Peoples.
Sometimes large rivers run through canyons as the result of gradual geologic uplift. These are called entrenched rivers, because they are unable to easily alter course. The Colorado River and the Snake River in the northwestern United States are two examples of this.
Canyons often form in areas of limestone rock. Limestone is to a certain extent soluble, so cave systems form in the rock. When these collapse a canyon is left, for example in the Mendip Hills in Somerset and Yorkshire Moors in Yorkshire, England.
The world's two largest canyons are the:
- Grand Canyon in Arizona, and the
- Copper Canyon in Chihuahua, Mexico
Other well-known canyon systems include:
- Cheddar Gorge in southwest England
- Hells Canyon in Idaho and Oregon
- Palo Duro Canyon in Texas
- Red River Gorge in Kentucky
- Royal Gorge in Colorado
- Cataract Gorge in Launceston, Australia
- Fish River Canyon in Namibia
- Colca Canyon along the Colca River in Peru
See also: list of landforms, geomorphology, geology, earth science.