92 



University of California Publications. 



[Geology 



tion of the great fault zone of the Sierra Nevada, the eastern por- 

 tion of the Lake Tahoe moat, and the western flanks of the 

 Virginia and Pine Nut ranges. Brief mention will be made of 

 a few localities off the map, as Mt. Rose, four miles northwest of 

 Slide Mountain, and the Truckee meadows west of Reno. Some 

 areal mapping has been done about Steamboat Springs just north 

 of the limits of the map, but the results are unnecessary in the 

 present paper. 



PETEOGEAPHY AND GEOLOGICAL EELATIONSHIPS. 



The number of rock species in the area is not great. They 

 play a small part in giving expression to the geomorphy but are 

 very important, particularly the later ones, in their relations to 

 the many orogenic movements which have occurred. 



Following the recognized classification, the rocks of the 

 region are: (See map, pi. 28). 



1. The Bedrock Complex, consisting of granitic and schis- 

 tose rocks. 



2. The Superjacent Series, consisting of volcanic intrusives 

 and extrusives, lake beds, river gravels, and recent alluvium. 



The Bedrock Complex. 

 The plutonic member of the older rocks is intrusive into and 

 hence younger than, the schistose rocks, and makes up much the 

 larger part of the exposed rock surface of the area. The schists 

 occur in isolated patches, two of considerable extent, over the 

 area. The size of these patches increases from north to south. 

 They represent the residual fragments of the roof of the great 

 Sierran batholith. Beyond the limits of the mapped area the 

 schists extend southward and occur also across Lake Tahoe, on 

 Mt. Tallac and southward. Southeast of the lake erosion seems 

 to have removed a larger proportion of them, due probably to the 

 greater elevation of the range in this locality. North of the 

 area shown on the map a large part of the hill south of Steam- 

 boat Springs is composed of the schists, the granite being there 

 intrusive into them. A still larger area is found making up the 

 most of Peavine Mountain, five miles northwest of Reno. West 

 of Lake Tahoe, on the Truckee quadrangle, these rocks are in 



