DISTRICTS OF DRY-FARM SOILS 77 
sulphate, or crystals of the ordinary land plaster. 
The fertility of the soils, however, is high, and when 
they are properly cultivated, they yield large and 
excellent crops. 
California district. — The fifth soil district lies 
in California in the basin of the Sacramento and 
San Joaquin rivers. The soils are of the typical 
arid kind of high fertility and great lasting powers. 
They represent some of the most valuable dry-farm 
districts of the West. These soils have been studied 
in detail by Hilgard. 
Dry-farming in the five districts. — It is interesting 
to note that in all of these five great soil districts 
dry-farming has been tried with great success. 
Even in the Great Basin and the Colorado River 
districts, where extreme desert conditions often 
prevail and where the rainfall is slight, it has been 
found possible to produce profitable crops without 
irrigation. It is unfortunate that the study of the 
dry-farming territory of the United States has not 
progressed far enough to permit a comprehensive 
and correct mapping of its soils. Our knowledge 
of this subject is, at the best, fragmentary. We 
know, however, with certainty that the properties 
which characterize arid soils, as described in this 
chapter, are possessed by the soils of the dry-farming 
territory, including the five great districts just 
enumerated. The characteristics of arid soils in- 
crease as the rainfall decreases and other conditions 
