GEOLOGY OF THE CO SO RANGE 



67 



height and character of Coso Peak are due in part to faulting; prob- 

 ably it is also near the original center- of the granitic dome. 



The granitic slopes descend on the east and disappear beneath 

 the alluvial apron. But there are several important facts to be noted 

 concerning this. In the slopes just west of Darwin the alluvium is 

 deeply trenched by present wet weather streams. This trenching 

 varies from a few feet in Coso Valley (see Fig. 3) to 75 feet or more in 

 the low hills. The same dissection of alluvial aprons and fans is 



Fig. 3. — View south over Darwin, showing low Coso hills at right, and fault 

 topography of Darwin Range to left. Wet- weather stream wash in middle distance 

 over Darwin. 



found along the east base of the Sierra Nevada as far north at least 

 as Carson City, Nev., and indicates a widespread climatic change. 

 The conditions of large, heavily loaded torrential streams have been 

 replaced by those of small, lightly loaded wet-weather ones. 



In the Coso hills the stream gulhes, locally termed washes, have 

 exposed the nature of the material lying upon the granite. The 

 surface layer is a coarse, angular, granitic sand, showing no traces 

 of water action. That lying lower, on the crystalline base, varying 

 in thickness from ten to thirty feet where seen, is stratified, and dips 



