PHYSICAL FEATURES OF COLORADO VALLEY 



39S 



by minor obliqixe and transverse flexures, while the general direction 

 of these ridges is as described, they are turned back and forth from 

 these lines in gentle or abrupt curves. These ridges are sometimes 

 low mountain-ranges. 



So, if we approach these mountains from either direction, north or 

 south, we first meet with ridges, or, as they are usually called in the 

 Westei-n country, hog-backs. In many places these are so steep as to 

 form a complete barrier to. progress. 



Usually the slope away from the side of the mountain corresponds 

 above with the dip of the rock, and is gentle or steep, as the dip is 

 lesser or greater. The side of the hog-back, next to the mountain, is 

 composed of the cut edges of the strata, and varies greatly with the 

 texture of the rocks; but usually it is steep or broken, sometimes but 

 tressed, sometimes terraced, sometimes columned and fluted. 



Fig. 6. a Stnclinal Vallet. 



On the south side of the Yarapa Plateau, near the head of Cliff"- 

 Creek Valley, there is an abrupt, oblique flexure, on the side of the 

 great fold, by which the rocks are turned up, so as to stand vertically. 

 In the rocks at this place there are two very hard conglomerates; the 

 intervening strata are soft sandstones and marls, and have been car- 

 ried away, aiul the conglomerates stand as vertical walls, 30 or 40 feet 

 in thickness, 50 to 300 feet in height, and several miles in length, and 

 between these is a broad avenue, or narrow vallev, beset with rao-o-ed 

 bowlders of conglomerate. 



The drainage of these narrow valleys between the hog-backs is not 

 always along their lengths, but the water is sometimes carried by 

 channels crossinof them and cuttings throuo;h intervenino; ridcres; hence 



