1921 ] Smiley: Flora of the Sierra Nevada of California 



LIMITS OF THE SIERRAN REGION 



California may be divided into six major provinces of which the 

 Sierra Nevada region is the second in size. The boundaries of these 

 divisions are not sharply defined, even the most clearly marked and 

 largest division, the Great Central Valley, rising gently to the north 

 and passing into the rolling foothills of the Klamath and Cascade 

 mountain systems. Of the other provinces, the Sierran region is the 

 best defined, being clearly limited on the west by the central valley 

 and on the east by the fault lines which are the chief structural 

 features of the range. The north and south limits are more or less 

 arbitrary: at the north the metamorphosed sediments of the Sierra 

 are seen to pass beneath the lavas of Lassen Peak just beyond the 

 North Fork of Feather River and this stream may be adopted as the 

 northern limit of the region-. 1 At the south the normally horizontal 

 Tertiary strata of the Sierra meet the folded sediments of like age 

 belonging to the Coast Range at Tejon Pass, and this line of contact, 

 which has been regarded as a fault, is generally accepted as the 

 southern boundary. 2 



The distance between these limits is about 370 miles in a northwest- 

 southeast line extending from the fortieth to the thirty-fifth parallel. 

 In width the Sierran region is quite unif onn : the distance from the 

 Sacramento Valley on the west to Honey Lake, lying at the foot of 

 the east slope in Lassen County, is about 80 miles, while near the 

 southern end, the distance across the range, through the High Sierra, 

 from the foothills bordering the valley of the San Joaquin east of 

 Tulare Lake to Owens Valley, is nearly 70 miles. The rectangular 

 region so defined has a base area of about 28,000 square miles. 



The heights of the several crests of the range vary from 6,000 to 

 8,000 feet at the north and south limits to over 13,000 feet in the 

 High Sierra, the average height of the watershed being approximately 

 9,500 feet. The ratio of the superficial area to the base area appears 

 never to have been estimated and varies considerably in different parts 

 of the range; in the mountains to the south of Yosemite Valley, a 

 region of bold relief, the surface is comparable in ruggedness to that 

 of the Alps and may exceed the base area by 60 to 100 per cent. 



Nearly all of the area covered by the present report lies above the 

 6,500-foot contour line, with which, in the north, the lower limit of th- 



