square feet in extent, but in drier desert regions they may be 

 several acres or even square miles in area. 



Although limestone is not as abundant in California as it is in 

 many other states of the United States, there are extensive out- 

 crops of this rock in various parts of the state and certain peculi- 

 arities in plant distribution are associated with these outcrops. 

 Although the rocks of the central Sierra Nevada are largely 

 rather sterile granitics, in the Convict Creek basin area between 

 Lee Vining and Bishop, Mono County, there are some marble 

 deposits located between 8,000 and 12,000 feet (2,438 and 

 3,658 m) in elevation. These alkaline rocks are mostly not for- 

 ested since there is rather little soil associated with them. How- 

 ever, in the creek basin there are several plant species occurring 

 on limestone that are slightly to extremely out of their normal 

 geographical range. Among these are Bear Berry , Arctostaphylos 

 uva-ursi, a low shrub of the heather family (Ericaceae), which 

 occurs otherwise in California only along the coast of the state 

 north of San Francisco Bay and is not known to occur elsewhere 

 in the Sierra Nevada; Kobresia myosuroides, a small sedge 

 (Cyperaceae) whose nearest populations are in the Wallowa 

 Mountains of northeastern Oregon and the Uinta Mountains of 

 Utah, and Scirpus pumilus, another small sedge whose other 

 populations occur about 750 miles away in the mountains of 

 Colorado and Montana. The explanation for these unusual plant 

 distributions associated with the Convict Creek basin marble 

 deposit is not clear, but it is apparent that in some way the pe- 

 culiar local soil allows these plants to grow in an area where 

 they otherwise would not be expected. 



In the arid regions of CaHfornia, subtle differences in soil 

 characteristics may have striking effects on the distribution and 

 nature of vegetation types and of plant communities. The various 

 soil types found in Cahfornia are associated with vegetational 

 effects that range from the undetectable to the very dramatic. 

 To illustrate the effect that soil factors may have in influencing 

 plant distribution, the vegetation of serpentine soils will be dis- 

 cussed in some detail. 



The term serpentine generally is appHed in Cahfornia to a 

 class of rocks that are essentially magnesium silicate. Serpentine 



25 



