162 



WATER 



are important factors in determining the amount of annual rainfall 

 in any region. In the continental United States the regions of 

 greatest rainfall are found in the northwest and in the extreme south- 

 east. Leaving out of consideration the effects of local topographic 

 features the amount of rainfall gradually decreases from Florida 

 toward the north and west, and from Washington and Oregon 



Fig. 69.— Forest vegetation, Norway and jack pines, Minnesota. (Photo- 

 graph by A. G. Gaskill. Courtesy of H. L. Shantz and the U. S. Department 

 of Agriculture.) 



toward the south and east. The region of least rainfall, on the other 

 hand, is found in the southwestern part of the United States and, 

 in general, it increases in amount from New INIexico and Arizona 

 toward the north and east. In much the greater part of the United 

 States the larger part of the rain falls in summer. In some regions of 

 the southwest, however, especially in southern California, the larger 



