230 



STRUCTURE COMMON TO ALL ROCKS. 



or even in some cases 12,000 feet, has given rise to the remarkable 

 series of north and south cliffs, which, together with the equally re- 

 markable east and west cliffs, due to erosion, to be described hereafter 

 (p. 270), form so striking a feature of the scenery of this region. The 

 accompanying section and perspective view (Fig. 197), taken from 

 Powell, shows several of these occurring in a distance of 90 miles. 



These fissures were formed by the elevation of the Plateau region, 

 and are parallel to the axis of elevation ; on each side of which they are 

 arranged with wonderful regularity. They were formed in very recent 

 geological times, probably late Pliocene and Quaternary,* and possibly 

 reaching even into the present epoch, and are therefore little affected 

 by erosion. Acid to this the nakedness of the rocks and the horizon- 



tality of the strata, and it 

 £.-— ^ is easy to see what an ad- 



& i \ mirable field is here af- 



/ \ forded for the study of 



faults. 



If such slips were 

 suddenly produced by 

 violent convulsion, then, 

 at the time of formation, 

 there must have been a 

 steep (Fig. 198) or some- 

 times even an overhanging escarpment (Fig. 196), equal to the dis- 

 placement. In some cases there is such an escarpment or line of steep 

 mountain-slope corresponding to the line of slip. 

 Plateau region the north 

 and south cliffs are pro- 

 duced by faults (Powell). 

 The Zandia Mountains, 

 New Mexico, are pro- 

 duced by a drop of 11,- _..-•""' 

 000 feet on the western 

 side, leaving an escarp- 

 ment still 7,000 feet high 

 (Gilbert). The precipi- 

 tous eastern slope of the 

 Sierra and western slope 

 of the Wahsatch are the 

 result of faults. In the Basin 



L 





=^ — : 



. 



i i i i i i" i i . T~pj 



---------_-_-"_ 



~-~-----~i^p 



. /.,;■>/ 



X£-I-I-3C-"-3f 



: ':^'.v: : :v" 



*.**=== 



•''■■• 









Fig. 198. 



In the Colorado 



Fig. 199.— Strata repeated by Faults. 



Range region also many of the ridges 

 are formed by faults. But in many cases there is no such escarpment, 

 the two sides of the fault having been cut down to one level by sub- 



* Dutton, Geology of the High Plateaus, p. 



35. 



