150 



University of California Publications. 



[Geology 



exists between the two sections of the hills bounding Washoe 

 Valley on the south, that could not have sunk under a condition 

 of compression. Also, the condition of the west end of the 

 Washoe Mountains indicates, not a compression, but a relative 

 tension, allowing the block there to sink a few hundred feet be- 

 low the adjoining ones east and southwest. The several move- 

 ments coincident with the first, or larger, east-west faulting, 

 seem to have elevated, relatively to the Washoe Mountains, the 

 two-mile square northwest of Lakeview, and to have produced a 

 similar and greater elevation of the high summits to the south 

 and west. This upward movement in the scpiare area is a second 

 factor causing compression along the east-west line of section. 

 On the other hand, since the formation of the diastrophic valleys 

 of Washoe, Eagle and Carson rests upon a tensile stress in an 

 east-west direction, and since the structure along the east-west 

 line through the Washoe Mountains is indicative also of tension, 

 it is believed that the connection between the Virginia Range and 

 the Sierra Nevada was established contemporaneously with the 

 formation of the present valleys. This would make the age of 

 the east-west faulting south of Washoe Valley contemporaneous 

 with one of the periods of the north-south motion, and thus earlier 

 than the two ages of east-west movements already discussed. The 

 direct actual evidence now in hand can carry us back no further. 

 The larger movements that have resulted in the grander physio- 

 graphic features are to be grasped only by an extended survey 

 over the larger region surrounding Lake Tahoe and the Virginia 

 Range. Yet there are a few general facts of structure and physi- 

 ography that will serve to establish a working hypothesis to guide 

 future investigation. These facts center about the badly faulted 

 Carson topographic area, and are briefly as follows : 



(1) The same general line of movement bounds Lake Tahoe 

 and the Carson topographic area on the north, and the Virginia 

 Range on the south. The Carson River follows this structural 

 break between the Virginia and Pine Nut ranges in its course to 

 Carson Sink. (2) The north-south line bounding the Virginia 

 Range on the west lies west of the line similarly bounding the 

 Pine Nut Range, or in other words, the Virginia Range has suf- 

 fered a relative displacement to the west. (3) The character- 



