PHYSICAL CHARACTERISTICS OF THE ARID REGION. 5 
THE ARID REGION. 
The Arid Region is the great Rocky Mountain Region of the United 
States, and it embraces something more than four-tenths of the whole coun- 
try, excluding Alaska In all this region the mean annual rainfall is insuf- 
ficient for agriculture, but in certain seasons some localities, now here, now 
there, receive more than their average supply. Under such conditions 
crops will mature without irrigation. As such seasons are more or less in- ’ 
frequent even in the more favored localities, and as the agriculturist cannot 
determine in advance when such seasons may occur, the opportunities 
afforded by excessive rainfall cannot be improved. 
In central and northern California an unequal distribution of rainfall 
through the seasons affects agricultural interests favorably. A “ rainy 
season” is here found, and the chief precipitation occurs in the months of 
December—April. The climate, tempered by mild winds from the broad 
expanse of Pacific waters, is genial, and certain crops are raised by sow- 
ing the seeds immediately before or during the ‘rainy season”, and the 
watering which they receive causes the grains to mature so that fairly 
remunerative crops are produced. But here again the lands are subject to 
the droughts of abnormal seasons. As many of these lands ean be irri- 
gated, the farmers of the country are resorting more and more to the 
streams, and soon all the living waters of this region will be brought into 
requisition. 
In the tables of a subsequent chapter this will be called the San Fran- 
cisco Region. 
Again in eastern Washington and Oregon, and perhaps in northern 
Idaho, agriculture is practiced to a limited extent without irrigation. The 
conditions of climate by which this is rendered possible are not yet fully 
understood. The precipitation of moisture on the mountains is greater 
than on the lowlands, but the hills and mesas adjacent to the great masses 
of mountains receive a little of the supply condensed by the mountains 
themselves, and it will probably be found that limited localities in Montana, 
and even in Wyoming, will be favored by this condition to an extent sufl- 
cient to warrant agricultural operations independent of irrigation. These 
