THE GREAT SIERRA NEVADA FAULT SCARP. 613 



of 1872. West of Mono Lake the total displacement can not be 

 less than six thousand feet, while farther south in Owen's Valley it 

 must have reached eight thousand to ten thousand feet, if not more. 



Following the first faulting in the Cretaceous outlining the re- 

 gion, occupied by the Sierra Nevada Mountains, the erosive agencies 

 began to work actively, for the area was undoubtedly high and 

 rugged. In the course of time the mountains were worn down in 

 places to an approximately base-leveled condition, and erosion almost 

 ceased. As a result of the renewed elevation in the latter part of the 



Glacial Rounded Bowlder, Head or Owen's River. 



Tertiary, rapid erosion was again inaugurated and the present deep 

 canons were excavated. While these canons on both slopes are ex- 

 ceedingly rugged, those on the east are very short, owing to the fact 

 that the crest of the range almost overlooks the fault scarp. Those 

 crossing this scarp have cut down nearly or quite to the level of the 

 upper part of the debris fan which has grown up at their mouths. 

 They are three thousand to five thousand feet deep, terminating 

 upward in cirquelike amphitheaters of precipitous rock. Through 

 the more rugged portion of the range the mountain peaks have 

 in many instances flattened, plateaulike summits which present a 



