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University of California Publications. [Geology 



TOPOGRAPHIC DIVISIONS. 



In this area there are three larger topographic divisions 

 or belts, running north and south. From west to east 

 these are ( 1 ) the eastern portion of the Sierra Nevada ; 

 (2) the level valleys at the east base of the Sierra; (3) 

 the western portion of the Virginia and Pine Nut ranges. The 

 first can be divided into the Tahoe moat, or down-dropped earth- 

 block, on the west, and the high ridge on the east. The depres- 

 sion caused by the sunken block is occupied by the lake west of 

 Carson, and by andesitic flows further north. This easternmost 

 part of the Sierra Nevada is call by Lindgren the Carson Range, 

 and is in this latitude the east crest of the Sierra Nevada proper. 

 It is characterized by the two highest peaks of the region, Mt. 

 Rose and Freels Peak, respectively, at the northeast and south- 

 east corners of Lake Tahoe. Both mountains rise nearly 11,000 

 feet above sea-level. 



From north to south in the area mapped, the Carson Range 

 is divisible into three parts. The northern part, bounded on the 

 south by an east-west line through the south end of Lake Washoe, 

 consists of a single high ridge with a lesser one just east, both 

 with straight, simple slopes east and west. The southern part, 

 bounded on the north by an east-west line through Glenbrook, 

 is composed of a single ridge with steep slopes in the east and 

 a gentle one to the west. The central part is made up of a med- 

 ley of comparatively small longitudinal ridges and valleys quite 

 different from the others. 



The second topographic division is composed of the three 

 connected valleys : Washoe Valley on the north, Carson Valley 

 on the south, and Eagle Valley in the center. Each valley is 

 opposite one of the three topographic divisions of the Carson 

 Range. Eagle Valley is the smallest of the valleys, east of the 

 widest of the three topographic divisions of the Carson Range. 

 Carson and Eagle valleys are separated by a low divide opposite 

 Prison Hill, inappreciable to a casual glance. Eagle Valley is 

 separated from Washoe Valley by a low ridge connecting the 

 Virginia Range with the foothills of the Sierra. Washoe Valley 



« Truckee Polio, U. S. G. S. 



