76 DRY-FARMING 
soil materials were washed from the mountains into 
the lake and deposited on the lake bottom. When, 
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 quantities, is not unusually 
abundant. The Great Basin soils are among the 
most fertile on the American Continent. 
Colorado River district.— The fourth soil district 
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 soils 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 part of the West. The rivers 
running through this district have cut immense 
eafions with perpendicular 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 
