186 



WILLIAM S. COOPER 



First of all, we have striking instances of the great difference 

 in precipitation which frequently occurs in California in stations 

 only a few kilometers apart. The greatest distance between 

 any two places listed here is 54 km. The series from Palo Alto 

 to Tunitas is especially interesting. In 1914-1915 the figures 

 for five stations along this line, one in each physiographic pro- 

 vince, were as given in table 1. It should be mentioned that 

 the two winters studied were seasons of more than average rain- 

 fall. The mean annual precipitation for Palo Alto is about 40 cm. 



It is also indicated that altitude is the main factor influencing 

 the ^amount of precipitation. The immediate vicinity of the 

 coast is relatively deficient as well as the interior valley. 



TABLE 2 



Further, returning to the hypothesis suggested on a previous 

 page, that difference in rainfall is responsible for the presence 

 of redwood forest in certain areas in the mountains and its 

 absence in others, we gather from the table the following evi- 

 dence. In both groups of rainfall stations — those with and those 

 without redwood forest — precipitation is abundant. In fact, 

 the stations without redwood forest are consistently a little 

 more rainy than those possessing it. Our hypothesis therefore 

 is unsupported ; rainfall difference is not here the deciding factor ; 

 and high precipitation alone is not sufficient to make possible 

 the development of redwood forest covering mountain slopes 

 away from streams. 



The explanation for the last statement is found in the long 

 dry season characteristic of the California climate. During 

 this critical period the soil everywhere away from permanent 



