CHAPTER I. 



THREE GEOLOGICAL PROVINCES. 



The Colorado Elver of the West drains a vast system of plateaus. On 

 'these plateaus are lone mountains, short ranges and groups of volcanic cones, 

 and the principal affluents of the river have their sources in high mountains 

 that stand on the rim of the great drainage basin. There is no considerable 

 valley along the course of the Colorado River north of the thirty-fifth par- 

 allel nor along the course of any of its principal tributaries. The streams 

 run chiefly in deep canons which, with other important topographic features, 

 serve to divide the area into plateaus. The district of country of which I 

 thus speak is, in its important characteristics, a plateau region. 



This plateau character was well recognized by Dr. Newberry. In his 

 report to Lieutenant Ives, page 41, he says: "The Colorado rises in a thou- 

 sand sources at an elevation of from ten to twelve thousand feet above the 

 sea, on the western side of the Rocky Mountains. Descending from their 

 fountain heads, its tributaries fall upon a high plateau of sedimentary rocks 

 which forms the western base of these mountains and occupies all the inter- 

 val between them and the great bend of the Colorado River where the river 

 enters the volcanic district already described;" and elsewhere in that vol- 

 ume he makes frequent mention of these characteristics. 



Mr. Blake, in the third volume of the Pacific Railroad Surveys, Part 4, 

 page 42, also mentions this topographic character as follows : 



"Extent of the table lands ivest of the Sierra Madre. This is a convenient 

 point from which to take a general view of the broad expanse of the great 

 plain that lies between the Sierra Madre and the mountains which form the 



