DAVIS: THE GRAND CANYON OF THE COLORADO. 



12' 



cliffs. It is crossed by the road leading from Kanab and Fredonia to 

 St. George. The divide does not here separate well-defined valleys, but 

 marks the boundary between two long and broad graded platforms of 

 gentle declivity, one slowly descending eastward and southeastward to 

 Kanab creek, the other westward to a dry branch of Virgin river. 



The eastern platform heads westward in a sharp slope or " wall " of 

 weak lower Triassic shales, two or three hundred feet high and locally 

 carved into bad-land spurs, forming a great westward curve, as if a large 

 bight had been gnawed into the head of the western platform, whose 

 border is appropriately concave. Evidently the eastern slope is gaining 

 area by undercutting the western. When we saw first this wall on 

 looking west from Pipe spring, it was perplexing, as there was no struc- 

 ture known in the lower Trias by which it could be explained ; and 

 moreover its even profile, descending gradually to the south, bevelled 



Figure 6. 



View from east of Pipe spring, showing "wall" of migrating divide in the background. 

 P, Pipe spring; T, Triassic plateau; L, landslide; S, Shinarump mesa; V-R, Sevier- 

 Toroweap f.iult-line. Constructed from map and sections. 



the gentle northern dip of the strata in a curious fashion (Figure 6). 

 But later in the day, when we looked northward to the divide from a 

 point on the road between Pipe spring and Mount Trumbull (S, Fig- 

 ure 6), the origin of the wall was easily discovered. The two graded 

 platforms were then seen in opposing profiles, the eastern heading under 

 the western, as in Figure 7. Indeed, the northern part of the western 

 platform could be seen to extend several miles eastward around the 

 head of the eastern platform, forming a bench that obliquely ascended 

 the front of the Triassic cliffs independent of structural guidance, un- 

 til it must have been a good thousand feet above the eastern plat- 

 form. I have never seen so fine an example of the relation between 

 two drainage slopes, one encroaching on the other. It was a disap- 

 pointment that our hurried movement made closer study of this area 

 impossible. 



