162 AGRICULTURE ON THE PACIFIC SLOPE 



At the south end of the San Joaquin Valley, near 

 Bakersfield, California, the yearly rainfall is only about 

 four inches, while at the north end of the Sacramento 

 Valley, near Redding, it is over twenty-four inches; 

 at Sacramento about nineteen only, at Fresno about 

 ten. So irrigation is most needful in the San Joaquin 

 Valley. In southern California, Los Angeles has about 

 fifteen inches of rain per year, Riverside about ten. But 

 there is much naturally moist or " sub-irrigated " land. 



From Cape Mendocino northward along the coast 

 the climate changes. There are summer rains, just 

 as in western Oregon and Washington. But east of 

 the Cascade Mountains in Oregon and Washington 

 there are rainless summers, as in California. In the 

 higher mountains thunderstorms (figure 80) bring rains 

 in summer when clouds gather around the peaks. 

 These are sometimes " cloud-bursts/ ' when the rain 

 falls so heavily that it cannot soak into the soil, and 

 rushes down the dry cafions, forming a wall-like wave 

 of water which sweeps all before it. In the lowlands 

 of California thunderstorms are quite rare. 



WEATHER IN OREGON, WASHINGTON, AND THE GREAT- 

 BASIN STATES 



As already said, heavy summer rains prevail on the 

 coasts of Oregon and Washington, west of the Cascade 

 Mountains, except that in the Willamette Valley there 



