1921] Smiley: Flora of the Sierra Nevada of California 45 



scheme of life-zones are still inadequate and their interpretation dis- 

 puted ; it may well be that conclusions deduced from present evidence 

 will, when the bases for deduction have broadened, become profoundly 

 modified if not abandoned. Nevertheless it now seems improbable that 

 the system of life-zones, elaborated by the investigations of so many 

 zoo- and phytogeographers, will be actually displaced even if in the 

 future other factors than those of tem^perature will be accorded greater 

 weight. 



In California there exist all the life-zones defined by Merriam 

 except the Tropical. The life-zones present vary greatly in extent: 

 the Lower Sonoran life-zone embracing the deserts of the southeast, 

 a small section of the southern coast, and the middle of the Great 

 Valley of California; the Upper Sonoran including most of the South 

 Coast Ranges, the inner slopes of the North Coast Ranges, and the 

 lower slopes of the Sierra on both its flanks ; the Transition extending 

 southward from a nearly state-wide belt at the north, along the sea- 

 ward slopes of the Coast Range as far south as San Luis Obispo 

 County and along the Sierra on both its flanks nearly to the Tehachapi 

 Mountains, with some outlying areas in the mountains of the southern 

 part of the state. In Plumas County this Transition flora is deeply 

 invaded by narrow east-west tongues of the Upper Sonoran flora and 

 in places becomes almost intersected, as at Beckwith Pass, where the 

 flora of the Great Basin sends a deep embayment into the northern 

 Sierra Nevada. The upper limit of the Transition life-zone marks 

 a real boundary; below it are found most of the plants generally 

 recognized as peculiarly Californian ; above it there is a constant 

 increase in the proportion of northern and widely ranging genera and 

 species. 



The region, the plant population of which is here considered, lies 

 on both flanks of the range above a line of varying altitude, rising 

 to the south and higher on the eastern flank. This line, which marks 

 the boundary between the rich temperate forest of the Transition 

 life-zone and the more varied, if less magnificent, vegetation of the 

 higher mountains, rises on the west flank from an elevation of about 

 6,000 feet in Plumas County to near 9,000 feet at the southern end 

 of the range; in the central Sierra (from the Blue Canon-Cisco line 

 south to Madera County) the boundary of the boreal region conforms 

 roughly to the 7,000-foot contour line. On the eastern slope of the 

 chain, the line rises from 6,500 feet west of Honey Lake to 9,500 feet 

 west of Owens Valley. Above this boundary, where the general aspect 



