16 University of California Publications in Botany [Vol. 9 



southwest of this interrupted height of land stretching from Bucks 

 Mountain to Sierra Buttes there are a number of distinct summits and 

 ridges rising to or above 6,500 feet — the very irregular crest north 

 and east of Onion Valley and curving southeast to include Pilot Peak 

 (7,505 feet) and Blue Nose Mountain (7,300 feet) ; the high ridges 

 about Mt. Fillmore (7,816 feet) and Rattlesnake Peak (7,000 feet) — 

 but they are separated by gaps of varying width and depression. 



The second of these north Sierran crests begins with Houghs Peak 

 (7,254 feet) and continues south through the Grizzly Mountains to 

 Grizzly Peak (7,578 feet) with westerly offshoots to Mt. Jackson 

 (6,625 feet) and Penman Peak (7,280 feet), south of which the 

 upper Middle Fork of Feather River cuts through to its head in 

 Sierra Valley. The third of the crest-lines is that which curves from 

 Mountain Meado^vs through the summit of Diamond Mountain (7,000 

 feet) and Thompson Peak (7,752 feet), running southeast past Honey 

 Lake and including McKesick Peak (7,083 feet) and Adams Peak 

 (8,200 feet). This third crest has a higher crest-line than either of 

 the other two but breaks down to below the 5,000-foot contour at Beck- 

 with Pass, where a gap of ten miles separates the 6,500-foot contours 

 on the north and south sides of the pass. 



Of these crest-lines only the first may be said to be continuous 

 with the high mountain region west of Lake Tahoe and this is inter- 

 sected by the deep but narrow caiion of the North Fork of North Fork 

 Yuba River. It has some significance for the study of the route by 

 which the "Glazialpflanzen" invaded the Sierras that only on the 

 northeast flank of this ridge are there well defined and extensive 

 glacial deposits comparable to those found in the mountains of Nevada 

 County and to the southward. 



The discontinuity in the high level surface at the north of the 

 range may have a bearing upon the colonization of the Sierra by rep- 

 resentatives of the boreal flora; within the range itself, once the 

 elevated region west of Lake Tahoe had been reached, these elements 

 were less hindered in their gradual occupation of the country yet the 

 progressive falling off in the number of species with high northern 

 affinities seen in going from north to south suggests that within the 

 range other gaps may occur across which the advance southward has 

 been difficult. These gaps, in addition to whatever significance may 

 attach to them in the study of plant distribution, are of interest to 

 all who traverse the higher mountains, since advantage is taken of 

 them to pass the divides and on the maps of the region they appear 



