36 DRY-FARMING 



North and east of the Great Basin is the Columbia 

 River Basin characterized by basaltic rolling plains 

 and broken mountain country. To the west, the 

 floor of the Great Basin is hfted up into the region 

 of eternal snow by the Sierra Nevada I\Iountains, 

 which north of Ne^'ada are known as the Cascades. 

 On the west, the Sierra Nevadas slope gently, through 

 intervening valleys and minor mountain ranges, 

 into the Pacific Ocean. It would be difficult to 

 imagine a more diversified topography than is pos- 

 sessed by the dry-farm territory of the United States. 



Uniform climatic conditions are not to be expected 

 over such a broken country. The chief determimng 

 factors of climate — latitude, relative distribution 

 (A land and water, elevation, jDrevailing winds — 

 swing between such large extremes that of necessity 

 the climatic conditions of different sections are widely 

 divergent. Diy-farming is so intimatelj' related 

 to climate that the typical climatic variations must 

 be pointed out. 



The total annual ]>recipitation is directly influ- 

 enced by the land topography, especiall}' l^y the 

 great mountain ranges. On the east of the Rocky 

 Mountains is the sub-humid district, which receives 

 from 20 to 30 inches of rainfall annually; over the 

 Rockies themselves, semiarid conditions prevail; 

 in the Great Basin, henmied in b)^ the Rockies on the 

 east and the Sierra Nevadas on the west, more arid 

 conditions predominate ; to the west, over the Sierras 



