10 Universiiy of California Fuhlications. [botany 



is of great importance, siuce a large percentage of it, percolating 

 throngh the soil and rock strata of the monntain, reappears at 

 lower altitudes, often in the form of springs, thus adding to the 

 supply of moisture for those regions. 



Geology. 



Concerning the geology of San Jacinto Mountain hut little is 

 known since, so far as we are able to determine, no geologist 

 has ever visited that region. It is probable, however, that it 

 was formed simultaneously with the San Bernardino and San 

 Gabriel Mountains, that is, during the middle Tertiary. 

 Throughout the Quaternary and early Tertiary a large land 

 mass occupied the region to the north and east of where these 

 ranges now stand, and it was from this that the supply of 

 material for the Southern California mountains was drawn. 

 After these were formed, a series of faulting took place on their 

 east and north sides, as is indicated by the steepness of those 

 slopes facing the Colorado and Mohave Deserts. 



The rock formation is almost exclusively granitic. At a few 

 places, notably on portions of Chalk Hill, the rock is largely 

 quartzite, while along some of the crests near Tahquitz Peak 

 and also along the east side a limited amount of volcanic rock is 

 found. Mica schists, gneiss, and some marble occur at a few 

 places, but not in large enough quantities to be of any great 

 importance. No limestone of any importance was found except 

 in the lower foot-hills. 



PLANT DISTRIBUTION ON SAN JACINTO MOUNTAIN. 



The Life Zones. 



Up to the present time the mapping of the life zones of North 

 America has been carried on chiefly by the zoologists, who have 

 considered its utility not only to the naturalist but also to the 

 farmer, since life zones run approximately parallel with croj) 

 zones ^'. It is evident that certain crops are adapted to certain 



*cf Merriam, "Life Zones and Crop Zones of the United States," in U. S. 

 Dept. Agr. Bull. Ix. (1898). 



