CANYON (Anglicized form of Span. cañon, a tube, pipe or cannon; the Spanish form being also frequently written), a type of valley with huge precipitous sides, such as the Grand Canyons of the Colorado and the Yellowstone livers, and the gorge of the Niagara river below the falls, due to rapid stream erosion in a "young" land. A river saws its channel vertically downwards, and a swift stream erodes chiefly at the bottom. In rainy regions the valleys thus formed are widened out by slope-wash and the resultant valley-slopes are gentle, but in arid regions there is very little side-extension of the valleys and the river cuts its way downwards, leaving almost vertical cliffs above the stream. If the stream be swift as in the western plateau of North America, the cutting action will be rapid. The ideal conditions for developing a canyon are: great altitude and slope causing swift streams, arid conditions with absence of side-wash, and hard rock horizontally bedded which will hold the walls up.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)