1921] Smiley: Flora of the Sierra Nevada of California 15 



water on freezing expands, causing lateral thrust upon the shores. 

 The result of many such temperature changes is to drag the rocks 

 upon the bottom or sides of the basin and ultimately shove them upon 

 the beach. 31 This process impedes the development of higher plant 

 life within the zone of drag. There is reason to think that the moun- 

 tain lakes affect the local climates, a subject considered later. 



The high mountain lakes are the catchment basins from which 

 issue the brooks that unite to form the many rivers draining the boreal 

 region. The drainage of the High Sierra may be divided into the 

 channel drainage, which prevails below tree-line, and the surface 

 drainage characteristic of the true alpine zone. In that zone the 

 surface of the ground during spring and early summer is, as a rule, 

 wet. The water derived from the snow-cover spreads out in the 

 shallow soil or trickles over the rocks and this condition of saturation 

 persists till the drifts are melted. Very gradually this percolating 

 water is gathered into small rills that feed the lakes and form the 

 sources of the great rivers of lower levels. With the disappearance 

 of the snow-cover a complete change is effected ; the shallow soil soon 

 dries out, the small vernal pools disappear, and a period of aridity 

 ensues only slightly ameliorated by the frequent light summer showers. 

 The vegetation in this alpine zone is then subject to a wet and cold 

 vernal period followed by a dry aestival phase. Near tree-line are 

 the beginnings of definite water channels. The high gradient of the 

 boreal region reduces all streams to typical mountain torrents broken 

 by cascades and rapids. 



Though mention has been made of a long axis of the Sierran region 

 about which the whole range has been slightly revolved, there is no 

 single crest-line throughout the summit region. In the north in 

 Plumas County the range has three crests. The western crest runs 

 from Bucks Mountain (7,231 feet) and Mt. Pleasant (7,111 feet) 

 through Spanish Peak (7,047 feet) with a crest continuously above 

 6,500 feet ; southeast from Spanish Peak the ridge line lowers, being 

 below 5,000 feet for ten miles before reaching Clermont Hill (7,014 

 feet). Here the Middle Fork of Feather River cuts through this axis, 

 which has its prolongation southward in the ridge, continuously rising 

 to or above the 6,500-foot contour line that runs from the head of 

 Camp Creek through Eureka Peak (7,490 feet) and Mt. Elwell (7,846 

 feet) to Sierra Buttes (8,615 feet). Between Clermont Hill and the 

 northwest end of this Camp Creek-Sierra Buttes crest, the gap below 

 the .6,500-foot contour is approximately nine miles wide. To the 



