76 DRY-FARMING 



soil materials were washed from the mountains into 

 the lake and deposited on the lake bottom. Wlien, 

 at length, the lake disappeared, the lake bottom 

 was exposed and is now the farming lands of the 

 Great Basin district. The soils of this district are 

 characterized by great depth and uniformity, an 

 abundance of lime, and all the essential plant-foods 

 with the exception of phosphoric acid, which, while 

 present in normal cjuantities, is not unusually 

 alxmdant. The Great Basin soils are among the 

 most fertile on the American Continent. 



Colorado River district. — The fourth soil cUstrict 

 lies in the drainage basin of the Colorado River. 

 It includes much of the southern part of Utah, the 

 eastern part of Colorado, part of New ^Mexico, nearly 

 all of Arizona, and part of southern California. This 

 district, in its northern part, is often spoken of as 

 the High Plateaus. The Sdils are formed from the 

 easily disintegrated rocks of comparatively recent 

 geological origin, which themselves are said to have 

 been formed from deposits in a shallow interior sea 

 which covered a large jiart of the West. The rivers 

 running through this district have cut immense 

 canons with perjjendicular walls which make much 

 of this country difficult to traverse. Some of the 

 soils are of an extremely fine nature, settling firmly 

 and requiring considerable tillage before they are 

 brought to a proper condition of tilth. In many 

 places the soils are heavily charged with calcium 



