Vol. 6] Eeid: Hie Geomorphogeny of the Sierra Nevada. 



135 



stream erosion and how much to the intersection of faults? 

 Aside from the fact that the streams are small and incapable of 

 carrying much load, the complete absence of alluvial fans at the 

 points where the creeks debouch upon the valley floor, indicates 

 that the stream erosion and deposition is a negligible factor. This 

 condition is precisely similar to that of Clear Creek. There is a 

 third well-marked cross fault-scarp just south of Genoa, of 

 which the upper part only is shown on the map. A similar par- 

 tial relative rotation of fault blocks appear to have occurred. 



The summit plateau remnant is broken by a number of faults, 

 both longitudinal and transverse. Genoa Peak is separated from 

 the crest line on both"north and south by the cross-fault already 

 noted, and the other faults are to be seen on the map. 



On the slopes westward from the summit the largest feature 

 that breaks the uniformity is a well-developed sub-crest composed 

 of a fault block west of Genoa Peak. This is exactly similar to 

 those west of Snow Valley Peak, and is well delineated on the 

 map. A well defined east-west cross-fault lies about a mile south 

 of Glenbrook. The long gentle slope east of Zephyr Cave ap- 

 pears to be broken by both longitudinal and transverse faults, 

 but not sufficient field study has been made here to warrant de- 

 tailed statements. 



Summation of Topography. — The east ridge of the Sierra 

 Nevada is thus divided into three distinct topographic areas. 

 The northern or Franktown area is characterized by two ridge 

 lines, a higher and a lower, separated by a structural longitudinal 

 valley. This longitudinal valley is divided into three topographic 

 parts, the southern one being subdivided into two portions. Each 

 of these divisions has its distinctive characteristics, due to the 

 various effects of differential movements in the rocks. The most 

 striking features are the many large and small fault blocks and 

 the hanging block in south Little Valley. The middle or Carson 

 area is characterized by three ridge lines, the center one forming 

 the range crest. Faulting is very complex, so that the east-west 

 profile shows a series of steps leading down from the summit 

 both to east and west. The long east slope is noted for a great 

 number of such step-faults. The main creeks flow in both longi- 

 tudinal and transverse valleys, of structiiral origin, and are 



