The United States as a Farming Country 31 
Fic. 18. Above the northern line marked 52° agriculture is not possible. A few crops may be 
srown, to a limited extent, in sheltered valleys opening toward the south; but in general people 
who live north of that line must depend on hunting, fishing, or mining for their living. 
Methods of farming used to offset unfavorable rainfall. In some 
parts of the dry regions large crops are grown by irrigation; that is, 
water is taken from the rivers by means of canals and is then led into 
little ditches in the dry but rich soil. The regions irrigated under 
the control of the United States government are shown in Figure 19. 
In other dry sections winler farming is practiced. Advantage is 
taken of the rains that come regularly in the winter, and a hardy 
winter crop is raised. 
In still other regions, especially those just east of the Rocky Moun- 
tains, the farmers make the most of the light rainfall by means of 
what is called dry farming. Before the rainy season begins, they 
plow the ground to let the rain soak in as much as possible. After 
the soil is wet they keep the surface finely pulverized with a harrow 
so that the moisture will not evaporate. Then, too, they are careful 
in selecting crops that can thrive on light rainfall, such as wheat, 
Kafir corn, and alfalfa. 
In these various ways the effect of unfavorable rainfall is partly 
overcome even in the dry West. Nevertheless, this section contains 
large deserts which cannot be used even for grazing, irrigation, win- 
ter farming, or dry farming. The driest and most barren of these 
deserts are in Nevada, southeastern California, Arizona, and Utah 
‘Fig. 22).