Editing Canyon (section)

==Formation==
[[File:Kevo Canyon.JPG|thumb|Kevo Canyon in [[Utsjoki]], [[Finland]]]]
Most canyons were formed by a process of long-time [[erosion]] from a [[plateau]] or table-land level. The [[cliff]]s form because harder [[rock strata]] that are [[resistance (geology)|resistant]] to erosion and weathering remain exposed on the valley walls.

Canyons are much more common in arid areas than in wet areas because physical weathering has a more localized effect in arid zones. The wind and water from the river combine to erode and cut away less resistant materials such as [[shale]]s. The freezing and expansion of water also serves to help form canyons. Water seeps into cracks between the rocks and freezes, pushing the rocks apart and eventually causing large chunks to break off the canyon walls, in a process known as frost wedging.<ref>
{{cite web
 |url=http://www.bobspixels.com/kaibab.org/geology/gc_geol.htm
 |title=The Geology of the Grand Canyon
 |access-date=2015-10-01
}}</ref> Canyon walls are often formed of resistant [[sandstone]]s or [[granite]].

[[File:Snake River Canyon Idaho 2007.jpg|thumb|[[Snake River Canyon (Idaho)|Snake River Canyon]], [[Idaho]]]]
Sometimes large rivers run through canyons as the result of gradual geological uplift. These are called [[entrenched river]]s, because they are unable to easily alter their course. In the United States, the [[Colorado River (U.S.)|Colorado River]] in the [[Southwestern United States|Southwest]] and the [[Snake River]] in the [[Northwestern United States|Northwest]] are two examples of [[tectonic uplift]].

Canyons often form in areas of [[limestone]] rock. As limestone is soluble to a certain extent, [[cave]] systems form in the rock. When a cave system collapses, a canyon is left, as in the [[Mendip Hills]] in [[Somerset]] and [[Yorkshire Dales]] in [[Yorkshire]], England.

===Box canyon===
{{For|the Colorado canyon|Box Canyon, Colorado}}
A '''box canyon''' is a small canyon that is generally shorter and narrower than a river canyon, with steep walls on three sides, allowing access and egress only through the mouth of the canyon. Box canyons were frequently used in the [[western United States]] as convenient corrals, with their entrances fenced.<ref name="encarta1">{{cite web |url=http://encarta.msn.com/dictionary_1861686591/box_canyon.html |title=box canyon |date=2009 |publisher=Encarta World English Dictionary |access-date=2009-08-04 |archive-url=https://web.archive.org/web/20091217053643/http://encarta.msn.com/dictionary_1861686591/box_canyon.html |archive-date=2009-12-17 |url-status=dead }}</ref>