rocks tend to be greenish or gray-green, rather glossy, and to 

 occur in outcrops that range from a few square feet to many 

 square miles in extent (Plate 3B). Serpentine outcrops are com- 

 mon in the North Coast Ranges of California, particularly in 

 Lake County, and reappear in many areas around the Bay Region 

 such as the Berkeley and Oakland hills. Mount Tamalpais, and 

 even the Presidio in San Francisco. South of the Bay, serpentine 

 is perhaps less common than northward, although extensive out- 

 crops occur near San Jose, at Pacheco Pass, and in the region of 

 Idria in San Benito County, and in various other portions of the 

 South Coast Ranges. Serpentine also occurs in various portions 

 of the foothills of the Sierra Nevada, and can be seen in many 

 areas near and along Highway 49. Although the raw outcrops are 

 generally greenish in hue, weathered serpentine and the soil de- 

 rived from it often are red. Many of the mountains in the state 

 named Red Mountain bear reddish soil derived from serpentine. 

 Serpentine is sufficiently distinctive and widespread in California 

 that in 1965 the legislature designated it as the official state 

 rock. 



The discontinuity between serpentine vegetation and the vege- 

 tation on adjacent non-serpentine soils generally is very striking 

 (Plate 3C). Where the two soil types meet, dense forest may give 

 way abruptly to open chaparral, or even to large expanses of 

 ground that support a few shrubs interspersed with occasional 

 herbs. In the North Coast Ranges, serpentine often supports 

 chaparral in a climatic region that, on other soils, favors the de- 

 velopment of coniferous forest. 



Serpentine soils are unproductive from an agricultural stand- 

 point. Few crops can be grown successfully, nor do the soils 

 support the growth of forage grasses for grazing animals. Since 

 trees usually occur only rather sporadically and thinly on serpen- 

 tine, such areas also are not useful for timber purposes. 



Characteristics of serpentine soils in California that are unfav- 

 orable to plant growth are: 



1 . Serpentine soils have a very low calcium content and a 

 correspondingly high magnesium content. Calcium and magnes- 

 ium are both essential nutrients in the metabolism of plants, but 

 plants are unable to take up sufficient calcium through their 



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