INTRODUCTION 



The Area Considered 



The region studied is designated in this report as the ' Yosemite region, ' 

 or, more precisely, as the 'Yosemite section.' It involves, as shown on the 

 accompanying map (pi. 62), a narrow rectangular area, 891/4 miles in 

 length by 17 1/^ miles in width. It reaches from the eastern margin of the 

 San Joaquin Valley eastward across the mountains to include the western 

 margin of the Great Basin, around Mono Lake, and thus constitutes a 

 typical cross-section of the central Sierra Nevada. The altitudes range 

 from 250 feet, at Snelling, to slightly over 13,000 feet, on Mount Lyell. The 

 total 'map' area is 1547 square miles. Yosemite Valley is included in its 

 entirety ; the Valley ends of the Wawona and Big Oak Flat roads are within 

 the ' section, ' as are the greater parts of the Coulterville and Tioga roads. 

 But neither the Mariposa Grove of Big Trees nor Hetch Hetchy Valley is 

 included. 



Within the limits of this 'section,' the members of our field party 

 traveled over most of the regular trails (routes are shown on the map) ; 

 in addition they sought out high points from which practically every square 

 mile of territory could be seen and mapped as to life zone. All together, 40 

 collecting stations were occupied by different members of our party. The 

 number of persons working at any one station at one time varied from 

 one to five. Certain camps such as those in Yosemite Valley, at Porcupine 

 Flat, on Tuolumne Meadows, and at the Farrington ranch were 'base 

 camps,' from which short trips were taken in different directions. At all 

 the places marked on the map as collecting stations, trapping for mammals 

 was done on one or more nights. 



Statistics of Field Work 



The first regular field work of the Yosemite Survey was a reconnaissance 

 trip by the senior author in the autumn of 1914. (Both authors were 

 already familiar with the lay of the land from previous visits to Yosemite 

 Valley and its environs.) Formal field work was instituted on Novem- 

 ber 19, 1914, and continued until January 9, 1915; it was commenced 

 again on May 15, 1915, and continued until July 31 ; it was again taken 

 up on August 16 and carried on until November 23 (1915). In 1916 

 continuous work was carried on in the neighborhood of Mono Lake from 



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