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University of California Publications in Geology [Vol. 8 



Most of the ranges lying around Cedar Mountain appear to be in 

 an advanced stage of physiographic development, like the latter. In 

 the Paradise Range to the north the physiographic aspect is also that 

 of a mountain mass which has undergone long erosion, but its degra- 

 dation has apparently not advanced to the stage exhibited by Cedar 

 Mountain. In that range, as in Cedar Mountain, a bolder summit 

 portion rises above the long, gentle slopes of the flanks. To the east, 

 across lone Valley, the surface of the Shoshone Mountains also indi- 

 cates an advanced stage of erosion. Beyond the Shoshone Mountains, 

 however, the summits of the Toyabe Range appear as a line of high, 

 rugged peaks, apparently representing a more youthful stage in the 

 physiographic cycle. From the Cedar Mountain territory views of 

 the ranges and valleys lying' to the south show the land surface to 

 be one of rather even aspect. The ranges have long slopes and appear 

 to be largely erosion residuals. It is a land surface such as would 

 be expected, not in the early, but in the later stages of an arid erosion 

 cycle, after a large part of the erosional lowering of the mountains 

 and of the filling of the valleys had been accomplished. 



The Gabbs Valley Range to the west is on the whole probably in 

 a middle or late mature stage. While long, gentle slopes predominate, 

 parts of the northern end are quite bold. The Pilot Mountains, which 

 are the southward continuation of the Gabbs Valley Range, are 

 bounded on both the east and west by steep escarpments, strongly 

 suggesting that this range has been deformed in late geologic time 

 by faulting of considerable magnitude along both its flanks. 



The ranges of the Cedar Mountain region are therefore not all in 

 the same stage of physiographic development. Cedar Mountain, with 

 its old-age surface, probably bears witness to a long period of little 

 disturbed erosion following the principal post-lacustral deformation. 

 This deformation had apparently produced a range of some elevation 

 relative to the bordering valleys, judging by the attitude of the 

 lacustral strata along its flanks, and this range was planed down 

 during the erosion period following the period of deformation. The 

 Gabbs Valley Range, on the other hand, is physiographically younger. 

 This may be due to the post-lacustral lavas which have been piled 

 upon it, or to deformative movements which may have affected it 

 subsequent to the principal post-lacustral deformation without ap- 

 preciably affecting Cedar Mountain, or to both causes. The erosional 

 history of the region in post-lacustral times has probably not been 

 simple, affected as it has been by lava extrusions and probable earth 



