244 J. E. SPURR^-ORIGIN AND STRUCTURE OF THE BASIN RANGES 



movement. Therefore Mr King* considered that the great ranges of 

 western.Nevada were thrown up at the same time as the Sierra. Whether 

 this disturbance was felt as far east as the Wasatch Mr King was unable 

 to tell, but he concluded that it was confined to the post-Carboniferous 

 continent, which extended from the Wasatch westward to longitude 117 

 degrees 30 minutes, and west of the continent through a strip 200 miles 

 wide, which included the present Sierra Nevada. The westernmost field 

 of the upheaval was, therefore, that of the most powerful compression. 

 Whether the disturbance was actually felt as far east as the Wasatch 

 Mr King could not decide. 



The approximate coincidence of the eastern limit of Jurassic folding 

 with the eastern boundary of the post-Carboniferous continent appears, 

 when considered by itself, very likely accidental. But the eastern 

 boundary of the post-Carboniferous (Mesozoic) continent, in Utah and 

 Nevada, seems to have coincided very nearly with the western boundary 

 of the Silurian-Devonian continent.f Moreover, in southeastern Nevada, 

 near the Utah boundary, the folded Basin ranges with their upturned 

 Tertiaries are separated from the comparatively undisturbed Colorado 

 plateau by approximately the same line, which was thus also the eastern 

 limit of the more important Tertiary distur])ances. Since early Paleozoic- 

 times, therefore, this north-and-south line has been a critical one in de- 

 termining regions of deformation and sedimentation. 



POS T- CR ETA CEO US MO VEME N T 



At the close of the Cretaceous, according to King,J the stress which 

 reelevated and folded the Rocky mountains produced its maximum dis- 

 turbance near the western edge of the area it involved, in the region of 

 the Wasatch, which was also near the western limit of Cretaceous sedi- 

 ments. That it was also felt farther west in the eastern part of the Great 

 basin, which had been part of the })ost-Carboniferous (Mesozoic) land- 

 mass, is rendered i)robable by the fact that during the succeeding early 

 Tertiary period this region suffered rapid and intense erosion, producing 

 part of the thick early Eocene sediments of Utah and eastern Colorado.§ 



In the western part of the Great basin the absence of Cretaceous rocks 

 ]irevents us from ascertaining whether this movement was felt. In tlie 

 Sierra Nevada || the Upi)er Cretaceous and Tertiary strata usually lie 

 nearly or quite horizontal ; west of the Sacramento valley, however, they 

 are generally deformed. 



♦Geological Explorations of (lif Fortiotli Parallel, vol. i, p. 747. 



tSee p. 242. 



tKing: Op. cit., p. 754. 



Dana : Manual of Geology, 4th edition, i)p. 359-304, 874. 



§ King : Ibid ; also op. oit., analytical map no. 4. 



II H. W. Turner • Seventeenth Ann. Rept. U. S. Geol. Survej', part i, p. 530. 



