1921] Smiley: Flora of the Sierra Nevada of California 23 



covering of snow has appeared though in exceptional seasons the 

 ground may still be bare (in the twelve years, this occurred five times 

 at Fordyce Dam, four times at Summit, three times at Tamarack). 

 By the end of November, at all three stations, the ground has become 

 covered except in very exceptional years (in the period under con- 

 sideration, the ground was bare of snow at the end of November in 

 two seasons at Fordyce and Summit, and once at Tamarack). The 

 beginning of December found the ground bare of snow once in the 

 period at all three stations and in the same season, that of 1907-08. 

 An extraordinary condition occurred in December, 1907, at Fordyce 

 and Summit, where, at the end of the month, no snow lay upon the 

 ground and but eight inches was present at Tamarack, 1,000 feet 

 higher. Even January first has found the ground at Fordyce free of 

 snow (season of 1910-11) and Summit with but four inches, though 

 Tamarack reported two feet. The winter of 1917-18 was unprece- 

 dented in the failure of precipitation; January first saw no snow at 

 Fordyce and Summit and but eight inches at the highest station. Even 

 as late as the first of February in this winter there were but two inches 

 of snow at Summit, a snowfall of over two feet which had occurred 

 about the middle of January having been almost completely melted 

 or evaporated. 



The conditions at Summit appear to be fairlj^ typical for the 

 Canadian zone throughout the Sierra. Melting of the snow-cover 

 proceeds at the rate of four inches per day at the middle of May. At 

 the beginning of June, 1911, there was about 38 inches of snow at 

 6-7,000 feet; by the twelfth, bare ground was visible in spots, and 

 within a week all snow was gone except in north-facing ravines and 

 on the higher peaks. *^ Here snow may linger till late in summer or, 

 after years of exceptional snowfall or in unusually cold summers, 

 persist in drifts throughout one season. Very rarely does such a drift 

 survive a second summer. On the summit of Mt. "Whitney, snow 

 drifts among the summit rocks last till the first of September.^^ 



Unfortunately there is no Hudsonian station, but the record at 

 Tamarack throws some light on conditions in the higher zone. The 

 snow-cover appears at Tamarack in the latter half of October ; by the 

 last of that month, on the average, 30 inches of snow has fallen and 

 winter has begun. "Spring" comes in the first or second week of 

 July ; by the middle of the month, the ground at 10,000 feet is com- 

 monly free from snow; the first of August finds only patches and 

 drifts in sheltered places. 



