Dry Farming and Irrigation 



Much of the water of streams and wells falls as rain Mountain 



in the mountains and flows either underground or above hy it ' is 



heavy 



SIERRA NEVADA. 

 51.18 In. 



PACIFIC 

 OCEAN 



18.44 "*& 



SACRAMENTO VALLEV 



19.78 in 





8e Level 25miltt W 75 



Gregory, Keller, and Bishop's "Physical Geography." Ginn & Co. 



FIG. 128. On mountain slopes that receive the wind from the sea, the rainfall 

 is very heavy. Near the summit it is heaviest. On the side of the mountains 

 away from the sea, the rainfall very rapidly diminishes. Note that at Colfax, 

 California, which is perhaps 32 miles to the west of the summit of the Sierras, 

 the rainfall is 47.02 inches, while at Reno, Nevada, which is about 30 miles to the 

 east of the summit, the rainfall is only 5.94 inches. 



ground to the lowlands. Highlands often receive 

 several times as much rainfall as lowlands, for the cold 

 air of the mountains is needed to condense the moisture 

 of the air into raindrops. The heaviest rainfall in the 

 world, five hundred inches annually (over forty feet), is 

 in the highlands of India. Figure 128 shows how the 

 rainfall in California depends on elevation. The same 

 air that blows across the Sacramento Valley, giving about 

 twenty inches of rain, gives forty-eight inches when 

 it has reached the summit of the Sierra Nevada Moun- 

 tains. At San Diego, on the coast, the rainfall is ten 

 inches a year, while upon mountains which are within 

 sight of the city the rainfall is fifty inches. Much of 

 this mountain rainfall would be wasted if it were not for 

 irrigation systems. 



The United States Reclamation Service is engaged 

 in reclaiming desert lands. Its work is on " govern- 



