144 



University of California Publications. 



[Geology 



treme youth ; on the east scarp the character of this profile be- 

 tokens a more mature erosion. (3) The valley line of the west 

 scarp is almost a straight line ; no valley lobes have been formed. 

 The east scarp presents a very wavy line at its meeting the val- 

 ley, due to the formation of a number of valley lobes. (4) Upon 

 the west scarp are youthful characteristics of a different order. 

 In north Little Valley there occurs the hanging block already 

 noted. This block depends directly- upon the east-west faulting 

 noted later, but indirectly it bears upon the age of the high west 

 scarp. The physiographic aspects of the scarp above and below 

 the level top of the small hanging block are not different, and 

 since the faulting which produced the hanging block is more re- 

 cent than the two longitudinal scarps under discussion (to be 

 shown later), the youth of the whole of the high west scarp is 

 established. Further, that part of the west scarp south of the 

 hanging block just mentioned shows another feature of import- 

 ance. This is the sliding of the broken and loose rock material 

 upon the steep slope, whose angle was greater than the angle of 

 rest of the incoherent rock. There is a further peculiarity in 

 that Little Valley has been produced in miniature at one place. 

 None of these features exist upon the east scarp, as the last ves- 

 tiges of any such, if they ever existed there, have long ago been 

 removed. 



More in detail, the profiles of the two groups of streams upon 

 the west and east scarps are thus delineated in figures 1 and 2. 



It is to be noted that the 

 west streams have not yet cut 

 downward into the scarp, while 

 the eastern ones have cut dis- 

 tinct gullies or small canons, and 

 developed the three distinct por- 



tions of a stream that has partly lost the characteristics of 

 extreme youth. 



The statement that the west scarp is but little degraded, while 

 the east one is much so, needs amplification. The process of ero- 

 sion of fault-scarps needs investigation, in order to establish 

 definitely the characteristics of a degraded fault-scarp. The 

 ideal conditions necessary to assume in this inquiry are actu- 



