8 University of California Puhlications . lbotany 



transverse cafions. The most important of these is that of the 

 North Fork of the San Jacinto River, the west wall of which 

 rises very rai)idly while the east side is somewhat more gentle 

 but still quite steep. The east arm, known as Dark Canon, is an 

 important branch heading- just below the main peak of the 

 mountain. The canons of the north side are exceedingly steep 

 in their upi)er portions, where the walls are largely of solid 

 granite, but below they descend more gradually and all ulti- 

 mately open into the main Snow Creek Canon. On the east, 

 those of the higher altitudes are of minor importance, but" the 

 lower half of this slope is gashed by steep canons, the walls of 

 which sometimes rise to a height of several thousand feet al)ove 

 the .streams at their bases. 



Soil and Climate. 



The nature of the soil of any region exerts a profound intiu- 

 ence on the character of the vegetation, but, on account of its 

 uniformity, it plays a minor role in the distribution of plants on 

 San Jacinto Mountain. On examination it is fouud to be 

 composed almost entirel.y of decomposed granite with a small 

 percentage of black mould near the surface, and is chiefly of a 

 loose, gravell.y texture. 



But little limestone is found on the mountain proper, 

 although there are several limestone quarries in the low" foot- 

 hills which continue the range to the west. Calciferous rocks 

 are also said to occur along the eastern base, and they are by no 

 means rare at various places along the south side, but the per cent 

 of lime in the soil is nowhere so great as to materially afifect the 

 character of the vegetation. Being derived from granitic rock, 

 in w^hich the feldsjiars form an important ingredient, the soil is 

 particularly rich in potash, while of the essential elements it is 

 probably the most deficient in nitrogen, since the supply of 

 humus, especially on the lower slopes, is very limited. 



On account of the aridity of the surrounding regions the 

 amount of humus in the soil of the lower foot-hills is almost 

 imperceptible, but at higher altitudes the ground is constantly 

 receiving deposits of pine needles and other organic matter, and 

 consequently we here find a thin huinus covering. At places 



