THE GREAT SIERRA NEVADA FAULT SCARP. 615 



tion of the Sierras, making more marked still the great fault on its 

 eastern side and differentiating it more completely from the region 

 to the east. From the Mohave Desert northward, the whole length 

 of the Sierras, these lines of weakness have given rise to an almost 

 continuous line of volcanic craters and flows. 



The Glacial period in the Sierra Nevadas was finally ushered in, 

 being doubtless due to the increased elevation in this enormous fault 

 block. Whether this period was contemporaneous with glaciation 



Glacial Lake, Head of Owen's River. 



in the East is not known. There are many things, however, which 

 lead us to believe that it was more recent here. Glaciers still exist 

 in the shadows of the higher peaks, and the facts that their scourings 

 are so fresh and the moraines so slightly modified are strong evi- 

 dences in favor of the view that the ice period terminated very 

 recently. The glacial phenomena about Mono Lake have been 

 studied by Le Conte and Russell, but farther south they remain 

 still almost unknown. Owen's River heads in the Sierras about 

 forty miles south of Mono Lake. It is a stream of considerable size, 

 draining a large basin, and issues from its rocky gorge at an eleva- 

 tion of eight thousand feet, thence flowing for many miles across the 

 elevated volcanic table-land. Because of the elevation the immense 

 glacier, which once gathered its strength in the basins of the fifteen 



