THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 31 



and southeast, by half as much in the other dimension. It is nearly 

 surrounded by the valleys of San Francisquito, Los Trancos, and 

 Corte de Madera Creeks, the floors of which range in altitude from 

 60 to 120 meters. The average height of the crest of the ridge is 

 approximately 180 meters, and the highest point, near the south- 

 eastern end, 246 meters. The mass here has a rather broad, rolling 

 summit, but the slopes are considerably dissected by ravines. North- 

 ward and northeastward from Jasper Ridge the hills are lower, but 

 southwestward, across the valley of Corte de Madera Creek, the 

 main front of the Santa Cruz Mountains rises to an altitude of 600 

 meters. 



The surface rock of the main part of the ridge is probably the 

 Chico sandstone of Upper Cretaceous age (14). There are two 

 areas of the Franciscan formation of considerable extent and one 

 outcrop of serpentine, but the area studied is entirely within the 

 limits of the presumptive Chico. This rock weathers into a uniform 

 coarse yellow sand. In most places the layer of residual soil is 

 very thin, but on a few level spots there is a greater depth. In 

 excavations in such places the sand is seen to merge gradually into 

 the undecomposed rock, which is found practically intact at a maxi- 

 mum depth of a meter or a little more. On steep hillsides the soil 

 is irregular in depth, with rock outcrops alternating with sand 

 pockets. The greatest accumulations are naturally at the foot of 

 the steepest slopes, where the sand contains many angular fragments 

 of considerable size. Of the ten stations studied, eight possess a 

 uniform soil of the type just described. The other two show local 

 differences which are of sufficient importance to affect considerably 

 the vegetation growing on them. 



At first thought it would seem absurd to devote a paragraph to 

 the climate of so limited an area as Jasper Ridge, after the climate 

 of the region as a whole has been discussed. In California, however, 

 such is not the case. One can not assume that the climates of two 

 places are alike because they are but a few kilometers apart. Witness 

 the great difference in rainfall already noted between Palo Alto 

 and the summit of the Santa Cruz Range. In the matter of rainfall, 

 Jasper Ridge lies between the above stations, as it does in position. 

 The precipitation for a number of stations in the Santa Clara Valley, 

 foothills, and Santa Cruz Mountains in the season 1913-14 (a very 

 wet year), was as follows (see 23, p. 185): 



cm. 



,, „ ( San Jose 47 . 83 



Valley: | Palo AltQ 62 15 



Foothills: Jasper Ridge 103 .71 



, , . . ( King's Mountain 169 . 25 



Mountains :{ Ben Lomond ; 197 66 



Assuming that the proportion between the stations will hold 

 roughly constant for a succession of years, the normal rainfall at 



