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University of California Publications in Geology [Vol. 8 



of active dissection of both the lacustral beds and the old-age surface 

 on Cedar Mountain during late geologic time is best explained by 

 uplift of Cedar Mountain and adjacent valleys relative to Gabbs Valley 

 and Big Smoky Valley, into which the detritus is carried. Climatic 

 fluctuations may have induced the intermittency of the cutting of the 

 different mesa levels, but it is believed that it has been relative uplift 

 in late geologic time which has determined certain areas, such as 

 Stewart and lone valleys, as areas of erosion and others, such as Gabbs 

 Valley and Big Smoky Valley, as areas of deposition. The date of 

 the beginning of this late deformation lies back in the Pleistocene, as 

 the cutting of the successive mesas has required some time. These 

 latest movements have perhaps been due to causes which were also 

 connected with the late faulting of the Pilot Range. 



The physiography of the Cedar Mountain region suggests, there- 

 fore, that, following the principal deformation occurring at about the 

 end of the lacustral period of upper Miocene time, a period of erosion 

 ensued. The degradation of Cedar Mountain and of the uplifted 

 portions of the adjacent valleys probably proceeded without inter- 

 ruption during the period, but the erosion of the Gabbs Valley Range 

 was disturbed by lava extrusion and perhaps by accompanying crustal 

 disturbances. Following this period of erosion, gentle warping has 

 occurred in late geologic, probably Pleistocene, time. 



If the period between the principal deformation of the upper 

 Miocene beds and the Pleistocene movement, i.e., roughly speaking the 

 Pliocene, was a time dominantly of planation rather than of defor- 

 mation, in the Cedar Mountain district, its Pliocene history roughly 

 parallels that of at least three other areas within the same broad 

 geologic province, namely, central Washington as referred to by Smith 

 and Willis, 11 southwestern Nevada as stated by Ball, 12 and the Mohave 

 Desert as announced by Baker. 1 :i 



11 Smith, G. O., Geology and Physiography of Central Washington; and 

 Willis, Bailey, Physiography and Deformation of the Wenatchee-Chelan District, 

 Cascade Eange, U. S. Geol. Surv. Prof. Paper, no. 19, 1903. 



12 Ball, S. H., A Geologic Reconnaissance in Southwestern Nevada and 

 Eastern California, U. S. Geol. Surv. Bull., no. 308, p. 41, 1907. 



is Baker, C. L., Physiography and Structure of the Western El Paso Eange 

 and the Southern Sierra Nevada, Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, no. 

 0, p. 137, 1912. 



