INTERMONT PLATEAUS OF THE PACIFIC 109 



over the whole tract down to the Mohave and Gila 

 deserts. 



The Great Basin of Nevada differs in aspect from that of 

 Oregon-Idaho, for countless short, parallel, rocky ridges 

 and bluffs, all running in a general north- south direction, 

 arise abruptly from its floor. Though rains be scarce, 

 the waters of the casual showers collect in the troughs 



Fig. 31. S;»ge-bi-ush Colorado. 



of the irregular surface, which they line with clay and 

 convert into evaporating pans, many of them covered 

 with layers of alkaline efflorescence and absolutely barren: 

 successive belts of succulent salt- bushes, rushes, grasses, 

 and shrubs surround them. Outside the saline flats, and 

 covering alike the valley plains, the gentle inclines of the 

 mesas, the rounded foot-hills, and the lower mountain 

 slopes, the very uniform vegetation consists almost 



