1914] Butvalda: 'Tertiary Mammal Beds in West-Central Nevada 355 



The eastern part of the Gabbs "Valley Range from Table Mountain 

 northward to Gabbs Valley is anticlinal in structure. It is separated 

 from the western part by a north-south depression which apparently 

 is largely synclinal in origin. 



PHYSIOGRAPHIC HISTORY 



The different ranges of the Cedar Mountain region are in some- 

 what different stages of physiographic development. Cedar Mountain, 

 viewed from a distance, as from the Gabbs Valley Range, has the 

 aspect of an old range which has suffered erosion for a long period 

 of time (pi. 37). Its slopes are for the most part long and even and 

 merge with the sloping valley sides. They are even, rock-cut surfaces, 

 whose evenness is only in small part due to aggradation of waste 

 materials. On close inspection the slopes are often rather rough in 

 detail, but viewed from a distance these smaller irregularities are 

 smoothed out and the flanks appear strikingly smooth. The higher 

 parts of Cedar Mountain consist of such summits as Little Pilot Peak, 

 surmounting the smooth sloping plain. The summit peaks are clearly 

 residual masses left standing by erosion above the relatively smooth 

 surface developed about their bases. The smooth surface is well 

 shown on the northern part of the range (pi. 38, fig. 1). It extends 

 in places over the summit portion and, as old valleys, between the 

 peaks on the summit. This smooth surface cuts soft and hard rocks 

 quite indiscriminately. Distant views of Cedar Mountain, showing 

 the smooth surface of the flanks and the residual-like type of its sum- 

 mit peaks, indicate that it is a mountain mass which was reduced 

 to an early old-age stage of topography. It is apparent that during 

 the development of the topography to this advanced stage the range 

 did not have its present relation of relief relative to the valleys on 

 either side, for the old surface is at present being dissected. This 

 dissection has not yet advanced far; it has only produced steep-sided 

 ravines or canons. Moreover, the old-age surface rises twelve to fifteen 

 hundred feet above the valleys, giving slopes down the flanks which 

 would appear to be steeper than graded slopes would be in the later 

 stages of the degradation of a mountain mass, even under arid condi- 

 tions. The steepness of the slopes and the fact that they are now 

 being dissected apparently indicates that the range has been deformed 

 in late geologic time. The lack of fault physiography and the general 

 form of Cedar Mountain indicate that the deformation was of the 

 general nature of an anticlinal uplift. 



