180 WILLIAM S. COOPER 



In the main body of the range redwood forest is the prevaihng 

 vegetation type. This great forest mass extends from near 

 Santa Cruz northward, covering the ridges and valleys of the 

 central part of the range with fair solidity as far as Butano Ridge. 

 North of this its extent is more limited and its continuity some- 

 what broken, the south facing slopes and ridge tops being clothed 

 instead with chaparral or grassland vegetation. At a point on 

 the main ridge directly west of Palo Alto the redwood forest 

 ends, chaparral, oak forest, and meadow sharing the region 

 northward. 



Obviously the main factor in the distribution of the redwood 

 is water in some form or other. In the Santa Clara Valley the 

 supply is hopelessly inadequate except along the banks of the 

 permanent streams. The same is true in a less extreme degree 

 of the two foothill regions and the coast. Turning to the moun- 

 tain region proper, a puzzling fact appears. Certain areas, 

 apparently not differing in topography and soil from nearby 

 ones which support luxuriant redwood forest, are practically 

 without these trees. The mass comprising Black Mountain 

 and Monte Bello Ridge is a conspicuous example. Even in the 

 deep caiions such as that of Stevens Creek, which surround and 

 penetrate the mass, redwoods are almost absent. The same is 

 true of the mountains and canons of the northeast face of the 

 range, southeastward from Black Mountain. These slopes and 

 valleys are farthest from the Pacific, and therefore a very natural 

 hypothesis to explain the absence of redwoods here is that it 

 is due to insufficient rainfall — quite certainly an adequate cause 

 in the case of the Santa Clara Valley and in the foothills. The 

 localities were conveniently situated, and therefore I attempted 

 to solve the problem by comparing the precipitation in nearby 

 areas, similar in topography and soil, some bearing luxuriant 

 redwood forest, some with none at all. 



Observations were not confined to the mountain region itself. 

 Rain gauges of a type shortly to be described were set out in a 

 group of stations, beginning at Palo Alto in the Santa Clara 

 ViLlley, and extending westward and southwestward across the 

 Santa Cruz Mountains to the ocean shore. I have arranged the 



