Vol. 6] Ecid: The Geomorphogeny of the Sierra Nevada. 133 



map. This ridge crest is flat, or nearly so, for a mile near its 

 south end, and descends to the north by a quite uniform slope. 

 The Tertiary river gravels are preserved upon the higher flat 

 portion, as shown in plate 25b. More careful inspection de- 

 velops the fact that a great number of cross-faults are present in 

 this ridge north of the flat portion, and that these faults have 

 allowed their north wall to drop relative to the south walls. The 

 north edge of the granodiorite bedrock under the gravels shows 

 well such a displacement, a small one of a few feet. East of the 

 east ridge the line of faidting is first shown by a steep and im- 

 pressive scarp, followed further east by the marked topographic 

 break west of Lakeview. The andesite area along the east-west 

 fault-line lies within the Carson topographic area and contains 

 the three ridge lines of that area. A view looking southward 

 over the gentle slopes west of the southernmost portion of Little 

 Valley is instructive. (See pi. 24b). In spite of the fact that 

 several buttress forms break the evenness of the profile, the whole 

 is strongly suggestive of a remnant of the old erosional surface 

 tilted to the east. This, combined with the propinquity of the 

 well-preserved plateau remnant near Marlett Lake and the 

 general topographic conditions of the region, makes such an 

 interpretation of the surface certain. 



The north portion of the Pranktown topographic area is de- 

 serving of special mention. Little Valley is terminated in this 

 direction as a physiographic feature by the strongly developed 

 east-west fault that bounds Slide Mountain on the south. The 

 great fault-scarp of this mountain rises almost perpendicularly 

 for 2,500 feet. It gives evidence of being the most recent scarp 

 of size in this part of the country. The name is sufficiently in- 

 dicative of the nature of this evidence. The biggest slide oc- 

 curred a few decades ago, and deposited many hundred tons of 

 rock in the canon. The small lake south of the mountain was 

 formed at this time. 



Structurally, Slide Mountain is a portion of the high west 

 ridge line, or the true summit of the range. The low east ridge, 

 so well developed in the Little Valley sections, is present on the 

 east flank of Slide Mountain at elevations from 6,500 to 7,600 

 feet. It is dissected by eastward flowing creeks and presents a 



