6o6 



JOHN LYON RICH 



even when the distance is six or eight miles. No suggestion of the 

 intervening valleys then appears. This close accordance indicates 

 that all the gravel-capped areas once formed parts of the same 

 even plateau-surface and have been separated only by subsequent 

 erosion. The plateau is still in the process^ of active dissection. 

 Adjacent parts are in many cases separated by valleys over i,ooo 

 feet deep whose tributaries, by working their way back into the 

 plateau by head-water erosion, are responsible for the very irregu- 

 lar ground-plan of the parts still remaining. Fig. 3 gives a good 



Pjq 2. — Miller Mountain plateau as seen from a distance of four and one-half 

 miles, looking west from the banks of. Salt Wells Creek. Note the even sky-Hne. 

 The view shows the edge of the plateau for a distance of five miles without disclosing 

 any visible irregularity. The conglomerate capping here averages between fifty and 

 one hundred feet in thickness and is well cemented at the base. The top of the plateau 

 is about 1,000 feet higher than the stream in the foreground. Between the stream 

 and the base of the scarps the wash-apron described on a later page is fairly well 

 shown. 



idea of the sky-line of the plateau as seen from a distance of about 

 four miles. 



Character of the rock floor of the plateau. — As already stated, the 

 entire plateau is capped by gravels which may be loose and uncon- 

 solidated in the upper part but are as a rule firmly cemented at 

 the base. This conglomerate capping varies in thickness from 

 eight to ten feet to as much as two hundred feet in different parts 

 of the area. The rock-surface on which it lies is a very even, 

 beveled rock floor which, though it may be slightly irregular in 

 places, is on the whole remarkably smooth. In no part of the 



