36 



University of California Publications in Botany [VOL. 9 



mountain divides receive more rain than the eastern slopes since the 

 storm winds come prevailingly from the west ; it is a common experi- 

 ence in the higher mountains to find shelter from driving rain by 

 descending some steep eastern slope. As regards soil moisture, how- 

 ever, the west slopes are, as a rule, less favored in the higher moun- 

 tains, partly because they are the insolated slopes in the warmer part 

 of the day and also because the winter winds sweep the snow over 

 the ridges and cause the deepest drifts to form on the east and north- 

 east facing slopes, where they persist longest in the summer and yield 

 moisture to the ground below. 



TABLE 1. MONTHLY TEMPERATURES, F. (MEANS AND EXTREMES) OF TRANSITION 

 STATIONS IN THE NORTHERN AND SOUTHERN SIERRA NEVADA. 



Summerdale, Mariposa County, 5,270 feet. 



110 

 100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



-LaPorte, Plumas County, 5,000 feet. 



\ 



Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. 



