146 A YEAR IN SCIENCE 



tains. This causes the dry summer season character- 

 istic of much of California. Along the coast of Wash- 

 ington the mountains are very close to the coast line, 

 and moisture is deposited where the winds strike the 

 high mountains. Washington, as ,a result, does not 

 have the dry summer season characteristic of the 

 southern part of the western coast. 



In the winter the land is cooler than the ocean; 

 consequently the winds begin to give up- their mois- 

 ture as they blow over the lowlands, and continue to 

 do so until they reach the Cascades in the north and 

 Sierras in the south. Beyond the mountains the air is 

 then dry. The winds descend and blow over the low- 

 lands and form the arid lands of the Great Basin, 

 eastern Oregon, and Washington. As the winds con- 

 tinue eastward they strike the Eocky Mountains where 

 they are again cooled and their moisture is deposited. 

 East of the Rocky Mountains as far as the Atlantic 

 these winds are dry, for they do not cross any more 

 high mountains and the temperature is not low enough 

 to cause" precipitation. East of central Kansas and 

 Nebraska the lands are well supplied with rain. This 

 rainfall is not due to the prevailing westerlies, how- 

 ever, but to cyclonic storms. 



The amount of rainfall in the United States varies 

 from over 60 inches per year along the coast of 

 Washington and Oregon and part of Florida, to less 

 than 5 inches in parts of Nevada, southern California, 

 Arizona, and Utah. 



