146 University of California Publications. [Geology 



accumulated material, the central portion gradually disappears, 

 worn away above and buried below. When this stage is reached 

 the profile is that of a hillside no different from any ordinary 

 one determined by erosion, with two segments, the upper con- 

 vex and the lower concave, as in figure 6. The stream courses that 



traverse a fault-scarp under the 

 assumed conditions follow the 

 usual law of erosion. If a scarp 



\show decomposed rock instead 

 of fresh, slides will occur that 

 Fig. 6. may modify somewhat the pro- 



files shown, but the results with only moderate alteration of the 

 wall can not differ essentially from those shown. At Slide Moun- 

 tain, for instance, where the scarp is in the first stage of degra- 

 dation, the great slides that have occurred have served only to 

 bring out more clearly the profile of a young scarp as given in 

 figure 3. 



In the region west of Washoe Lake all the various profiles can 

 be found well developed. The oldest stages are most clearly 

 shown on the scarp east of Little Valley. Here the profile of 

 three distinct segments is present, and indicates a greater age 

 than the west scarp. The actual profiles are given in figures 7 

 and 8 for comparison. 



A glance at the map is sufficient to 

 convey the fact of greater dissection of 

 the east scarp by streams, and forma- 

 tion of small valley lobes. This is all 

 Fig. 7. Fig. s. the better evidence of relative ages, be- 



cause of the smaller streams flowing on the east scarp. A perti- 

 nent question here is one concerning the origin of all the stream 

 gullies on the east scarp. Transverse faulting may be a factor, 

 and probably is to some extent. But this being so, the greater 

 age of this scarp is the more clearly presented. 



The bearing of the hanging block has been sufficiently dis- 

 cussed. 



From the above facts and principles, it is concluded that the 

 two fault-scarps associated with Little Valley are of different 

 ages and therefore represent two periods of north-south faulting; 



West 



