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University of California Publications. 



[Geology 



lightest and finest on the lowest, with progressively more ad- 

 mixture of alluvium with decreasing elevation. It is possible 

 that faulting is responsible for the three terraces, but no definite 

 facts have been found to establish this. They are very sugges- 

 tive of a series of small but distinct elevations of the Sierra in 

 very late geologic time, comparable to the warping and tilting 

 of Washoe Valley. 



The second notable point concerning the Carson River is one 

 relating to the Virginia-Pine Nut Range. Near Empire the river 

 flows rather sluggishly before it enters its canon ; within the 

 rocky gorge it is cutting in solid rock. A mile east of Empire, 

 river gravels and deposits are found on the hillsides up to 300 

 feet above the river. The whole canon has not yet been ex- 

 amined, but the known facts indicate an elevation of the range, 

 with resultant downcutting of the river. The rocks here are 

 largely volcanic and are eroded by the river at as rapid a rate 

 as the elevation of the range. 



In the Truckee Meadows north of the Carson quadrangle the 

 terraces and antecedent stream features of the Truckee River are 

 more marked than those of the Carson. There are three well- 

 developed terraces west of Reno, besides a few smaller and 

 obscure ones. The lowest has the angle of slope of the present 

 river, while the others incline more steeply to the east, the higher 

 having the greater grade. The two older terraces have been 

 broken and displaced with the downthrow of twenty-five feet to 

 the east by a north-south fault in the range south of the river. 

 The upper terrace contains a vast amount of very coarse rock 

 fragments, boulders five or six feet in diameter being not rare. 

 It was probably formed in late glacial time when the river was 

 transporting glacial morainal material from its canon near Lake 

 Tahoe. This indicates a late age for the faulting, coincident with 

 the later periods of movement in the Carson area. The Truckee 

 River flows almost due east across the meadows near Reno, and 

 enters the Virginia Range in a manner similar to the Carson. 

 But here exists evidence sufficient to establish the fact of eleva- 

 tion of the Virginia Range. For a mile before the river meets 

 the mountains it flows very sluggishly in a deep channel bordered 

 by swampy ground. West of this its grade is considerable and 



