84 EXTINCT AND VANISHING MAMMALS 



regain a foothold." Twelve years later Grinnell and Storer 

 (1924) reported that the protection thus accorded was effec- 

 tive "and the prospects for their perpetuation are now bright." 

 Indeed, by 1920 they had so increased as to become troublesome 

 at Snelling, through interfering with irrigation works. In the 

 river basins of western California, these beavers feed princi- 

 pally on the bark of willow and cotton wood. At the present 

 time they are found in some numbers in the extreme western 

 end of the Yosemite section, along the lower courses of the 

 Merced and Tuolumne Rivers west of the foothills. With 

 proper management it is expected that this population may be 

 maintained in localities where it does not interfere with human 

 activities. This seems especially desirable, since the golden 

 beaver is one of the better-marked races of North American 

 beavers. 



A very thorough account of this beaver in California has 

 been published by Grinnell, Dixon, and Linsdale (1937, vol. 2, 

 pp. 629-721) in their recent work on the "Fur-bearing Mam- 

 mals of California." They find that it is more a "bank" 

 beaver than most of its relatives, adapting its habits to life 

 along sluggish lowland streams. The largest specimen of 

 which there is authentic record weighed no less than 82 pounds. 

 They indicate that because of individual variation the shape 

 of the tail is of less diagnostic value in the discrimination of 

 races than had hitherto been supposed, and further it appears 

 from measurements of a series of fresh specimens that in males 

 its width is proportionally greater than in females. The 

 period of gestation is about three months, and two to four 

 young is the usual number per litter. Beavers in California 

 are now "just about free from any natural enmy," with the 

 reduction of bears, mountain lions, and river otters. Although 

 the number of beavers in a given locality is often overestimated, 

 these authors believe that in 1920 there were about 250 inhab- 

 iting 15 square miles of river bottom in the vicinity of Snelling. 

 Trapping on the San Joaquin River near Mendota in the same 

 year indicated about 12 animals to the square mile. On this 

 basis it was calculated that in 1921 there were about a thousand 

 golden beavers in California. Much of the area formerly 

 inhabited by beavers is now reclaimed and in use for agricul- 

 tural purposes in the delta region, so that the beaver's range 

 has become more and more restricted, and by 1911 very few 



