CANON, kti-nyr,re or, Engl. prom, knn'yon, or CANYON (Sp. anion. calm, tube, funnel, can non). A tern) applied in the United States to a deep and extensive ravine along a watercourse. Canons are formed by the erosive action of rivers on their beds, and are usually limited to the upper portions of basins, where the water flows with considerable velocity. They are typical of dry climates and of plateau regions which have been elevated in comparatively recent geological times. In moist climates rock decomposition and denudation keep pace with erosion, and the com bined action of these agencies leads to the carv ing out of broad, open valleys, a result which may he produced after a very long period in a dry cli mate. lint, unless the slope of the river-bed has been greatly reduced, the erosive action of the water in regions of small rainfall will be more effective than the atmospheric agencies, and con sequently the walls of the channel will have a precipitous character. The nature of the rock
over which the river flows is also a factor in the formation of canons; hard rocks usually decom pose slowly, and thus preserve the contours of the channel as originally determined by erosion. There are many canons in the western part of the United States, the most notable being the Grand Canon of the Colorado, which is more than 300 miles long and has almost vertical walls from 3000 to 7000 feet in height. The Rio Grande and Yellowstone have similar hut less extensive canons. the name is sometimes ap plied in the Western States to the narrowing and deepening of the channel as a river crosses a mountainous barrier, but in such instances it does not differ from a gorge. See RIVER; Cill.0 RAM) RIVER; YELLoWSToNE NATIONAL PARK; etc.