PREFATORY I^OTE. 



BY THE DIRECTOR OF THE SURVEY. 



The Colorado Plateaus extend from southern Wyoming through 

 western Colorado and eastern Utah far into New Mexico and Arizona. 

 They are bounded on the north by the Wind River and Sweetwater 

 Mountains, on the east by the Park Mountains, on the south by the Desert 

 Range Region, and on the west by the Basin Range Region. 



The Plateaus are chiefly drained by the Colorado River, but a small 

 area on the northwest is drained into Shoshone River, another on the north- 

 east into the Platte River, still another on the southeast into the Rio Grande 

 del Norte, and finally the western margin is drained by the upper portions 

 of the Sevier, Provo, Ogden, Weber, and Hear Rivers. The general eleva- 

 tion is about 7,000 feet above the level of the sea— varying from 5,000 to 

 12,000 feet. The ascent from the low, desert plains on the south is very 

 abrupt — in many places by a steep and almost impassable escarpment In 

 the Plateau Province an extensive series of sedimentary formations appear, 

 embracing Paleozoic, Mesozoic, and Tertiary strata, but crystaUine schists 

 and granites are found in some of the deep canons. 



A marked unconformity exists between the Silurian and Devonian 

 rocks; another between the Devonian and Carboniferous; another, but 

 not so well marked, between the Carboniferous and Mesozoic, and lastly 

 an unconformity between Cretaceous and Tertiary is usually well defined. 

 The Plateaus have been above the sea since the close of the Cretaceous 

 period but during early Tertiary times extensive lakes existed through- 

 out tlie Province. In Mesozoic and Tertiary times the Basin Province to 

 the west was the principal source of the materials deposited in the Pla- 



