646 ANIMAL LIFE IN THE YO SEMITE 



The Pacific Rattlesnake is the only poisonous animal to be found among 

 the vertebrates in the Yosemite section, and the experience of the great 

 numbers of visitors to the region has shown that there is little real danger 

 from even this animal. 'Rattlers' are to be found from the plains of 

 the San Joaquin Valley eastward into the mountains to an altitude of 

 8100 feet, though they are more common in the foothill country than at 

 the higher levels. Yosemite Valley originally had a fairly large population 

 of rattlesnakes, but these reptiles have been pretty well eliminated there, 

 by the hand of man, within the past two decades. On the east slope of 

 the Sierras, between the Yosemite region and the neighborhood of Lake 

 Tahoe, rattlesnakes appear to be wanting entirely, though they are present 

 farther east in the Great Basin territory. 



The danger from rattlesnakes is often exaggerated. This is not to say 

 that their bite is not poisonous, for that has been proved beyond doubt. 

 But the rattlesnake is ordinarily not an aggressive animal and when met 

 wuth will usually try to escape if not cornered. Very few persons are 

 actually bitten and of those who are bitten but a small percentage succumb, 

 as in most cases prompt application of proper treatment counteracts the 

 effect of the poison. 



The extreme size attained by the Pacific Rattlesnake in the Yosemite 

 region is not known with certainty. Exact measurements of freshly killed 

 individuals are scarce. Occasionally rattlers measuring as much as 5 feet 

 from tip to tip are killed in the foothill country, according to Mr. Donald 

 D. McLean. The largest example obtained by our party measured 36 

 inches (915 mm.) in length. The average length of the rattlers in the 

 region is probably slightly under this. Measurements from skins, either 

 fresh or dried, are of but little service save to indicate the general size 

 of the snakes from which they were taken. Such skins may be, and often 

 are, stretched from 10 to 25 per cent beyond the dimensions of the reptile 

 'in the flesh.' 



The head of the rattlesnake is bluntly triangular in outline and sharply 

 set off by the relatively slender neck (pi. 5dh). This shape of head, though 

 always to be found in the rattler, is not a reliable character for distinguish- 

 ing poisonous snakes generally from harmless ones. The garter and gopher 

 snakes, both harmless species, are able to assume this form of head tempo- 

 rarily. The head of the rattlesnake shows other distinctive features: the 

 upper surface is devoid of large plates, being covered with small scales; 

 there is a distinct pit between the nostril and the eye; and the pupil of 

 the eye is vertically elliptical. The body of the rattlesnake is usually thick, 

 perhaps 5 inches in circumference in a large example. The scales on the 

 body of the snake are large and coarse and each scale is surmounted by 

 a conspicuous lengthwise ridge or keel. The tail is (luite short and bears 



