68 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



White. On average, this slope may be said to be less than 200 feet to 

 the mile. Short grass covers many of the ridges along their flat tops, 

 while the sides are grown over in part by juniper and pifion. This gen- 

 eral character holds good as far west as Evacuation Creek. Near the 

 junction of that with the White it changes, however. A heavy series of 

 superincumbent sandstones has produced a change here. Marching 

 down the creek, we remain for a long distance in an unbroken caiion, the 

 walls of which are about 600 to 800 feet high. Four miles above its 

 entrance into the river the trail leaves the creek, and, ascending to the 

 summit of the long ridge west of it, strikes across toward a sharp south- 

 erly bend of the White. From there downward the river flows in a 

 narrow canon.- Walls, averaging 1,000 feet in height, enclose it on 

 either side, presenting almost vertical faces. A dark-brown to yellow- 

 brown sandstone, regularly bedded, composes them. Erosion has here 

 produced numerous fantastic figures that a lively imagination can en- 

 dow with life, and readily compare with animate beings. On the isolated 

 hills and knolls south of the cai5on, which former owe their existence 

 to remnants of this sandstone, " monuments '' of all kinds can be found. 

 Cleavage-planes in the sandstone strata have produced innumerable pic- 

 turesque forms, and erosion, both by water and sand, has been the 

 artist who shaped the original block. 



For about thirty miles this caiion continues. The bed of the river is 

 narrow, covered with shfubs and brush, which greatly impede the progress 

 of man and animal. Dry washes coming from the north are cut deeply 

 into the yielding sedimentary beds. Throughout the district, wesl of 

 the Great Hogback, the topographical features of the region are remark- 

 ably uniform. " Like cause produces like effect" finds another applica- 

 tion here. We find but very subordinate changes in the lithological 

 constitution of the sedimentary beds, and in accordance therewith we 

 notice that the general features observed undergo but slight changes. 



As a rule, it may be stated that the shales and marls, whenever suffi- 

 ciently comnact, have produced steep, inaccessible cliffs, while the sand- 

 stones and sandy shales form more gentle slopes. Sandstones, mostly, 

 can be found as the capping of low bluffs, which they have protected 

 from erosive influences, thus giving rise to their formation. 



Many detail features, due partly to erosion, partly to vertical cleavage 

 of the strata, were noticed, and will be referred to at the proper jjlace. 

 Inasmuch as certain geological formations comprise similar or identical 

 strata (liihologically speaking) within circumscribed areas, occurrences 

 of such a nature may, locally, be regarded as characteristic of well-de- 

 fined geological groups. Viewing the subject from this standpoint, the 

 "monuments" and other minor orographic features becojne of import- 

 ance to the geologist exploring. 



In the subsequent pages space will be devoted to a short discussion 

 of the influence that stratigraphy and the lithological character of strata 

 have UDOu the orography in general, and upon that observed in Colo- 

 rado in particular. To the field-geologist, who is required to accomplish 

 his work with as much accuracy as possible in a very short time, hints 

 furnished by exterior physical appearance are of the greatest value. 

 Colorado, perhaps more than many other regions, furnishes excellent 

 material for a consideration of this subject, and at the end of the report 

 on that State a brief treatise thereupon may justly find its place. 



VEGETATION. 



Each special region of the country has its own more or less charac- 

 teristic shrubs and trees. In the low valleys and along the plateau-like 



