1921] Smiley: Flora of the Sierra Nevada of Calif or ma 



21 



of the summit region varies from about 70 inches in Plumas County 

 to 47 inches at Summit and probably 40 to 30 inches west of Owens 

 Vallej''. Above the zone of maximum rainfall on the western slope 

 there appears to be a fairly constant decline with increasing altitude, 

 amounting to 0.40 inches per 100-foot rise. On the eastern slope the 

 crest is the altitude of greatest rainfall and there is a constant decline 

 to the floor of the Great Basin and of Owens Valley. Between Sum- 

 mit and Boca the rate of decrease is approximately 1.85 inches per 

 100 feet of descent. In the southern Sierra, Lee*° found the rate to 

 be about .40 inches per 100 feet. 



The rainfall of the Sierra is markedly seasonal ; winter has the 

 maximum amount and summer the minimum. In this strict seasonal 

 distribution of precipitation the Sierra is peculiar among the high 

 mountains of western America. Table 4 shows the graphs for repre- 

 sentative Transition and Boreal stations. There appear to be two 

 winter maxima: a major in January and a minor in March. Aside 

 from the small amount of rain falling on the eastern side there is the 

 further difference that this amount is more evenly distributed through- 

 out the year; the graph for Bodie is flatter than that of any other 

 station. A feature of the high mountain rainfall, contrasted with that 

 of the Transition life-zone, is the more copious summer showers; at 

 LaPorte and Summerdale, July and August are practically rainless, 

 while Bodie has over half an inch and Tamarack nearly an inch in 

 July. 



SNOWFALL 



Records of snowfall in the Sierra from the central division cover 

 a period of over forty years; at Summit there is a continuous record 

 since 1870. At that station 86 per cent of the total precipitation falls 

 as snow.*^ The total seasonal fall varies within wide limits about a 

 mean of 443.5 inches. During the period of record at Summit the 

 extremes in five seasons were : 



These maxima are among the largest, if not the largest, ever reached 

 in the United States.*- 



