Effect of More Rain 
45 
erosive forces of desert lands. The main stream-courses are 
thus in the lower arid regions and in sedimentary formations, 
while their water-supply comes from far away. The deepest 
gorges, therefore, will be found where the rainfall is least, un¬ 
less diminishing altitude interferes. Thus the greatest gorge 
of the whole basin, the Grand Canyon, is the one farthest from 
Pinnacle in the Canyon de Chelly. 
About 1500 feet high. It is much wider from the side. 
Photograph by Ben Wittick. 
the sources of supply, and in the driest area, but one, of the 
whole drainage system. It ends abruptly with the termination 
of the high arid plateau which made it possible, but had this 
plateau extended farther, the Grand Canyon would also have 
extended a similar distance. It is plain then that the cutting 
of these canyons depends on the amount of water (snow is 
