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University of California Publications. [Geology 



therefore consequent. Marlett Lake, with the down-dropped 

 block, is present in this area. The south area is characterized by 

 one ridge line, forming the crest, a magnificent fault-scarp on 

 the east, and a comparatively gentle slope on the west. Genoa 

 Peak, the highest point, lies on the east-west edge of a wedge of 

 granodiorite that has been rotated about a north-south axis in 

 such way that the high edge has moved eastward relative to the 

 base. Other transverse and longitudinal faults occur also. One 

 small sub-crest is found on the west slope overlooking Lake Tahoe. 



IV. The Valley Zone. 



The Nevada valleys lying at the east base of the Sierra 

 Nevada present some physiographic and structural features of 

 importance to the geomorphogeny of the region. The three 

 valleys, Washoe, Eagle, and Carson, are structurally one, and 

 were the east front of the Carson topographic area forced back 

 to the line of the areas north and south there would be but 

 one continuous valley from Washoe to Genoa. Near the former 

 place andesite flows mask the granodiorite outlines. The instruc- 

 tive features in Washoe Valley are connected with the lake. This 

 body of water lies on the east side of the valley, at the foot of 

 the hills of the Virginia Range. The present lake basin is con- 

 tinuous to the north end of the valley, where a discharge occurs 

 at periods of high water. A low divide is present between Washoe 

 Lake as mapped and the small body of water at Washoe station. 

 This feature is significant, as will be shown later. Prom the 

 smaller lake a creek flows northward through a sharp-cut though 

 shallow canon in volcanic agglomerate and eventually reaches 

 the Truckee River. Directly west of Washoe Lake and south 

 of Franktown several streams have cut trenches over ten feet 

 in depth in the valley at the foot of the Sierra, and have exposed 

 a series of lake beds. The same beds are exposed along the rail- 

 road track at Washoe and south for about a mile. The beds south 

 of Franktown dip slightly to the east ; those at Washoe dip south- 

 easterly at a few degrees. From Franktown south there is also 

 a well-preserved lake cliff cut in the above mentioned sediments. 

 This cliff follows approximately the line of the railroad a short 

 distance east of it. North of Franktown its presence is not yet 



