650 ANIMAL LIFE IN THE YOSEMITE 



to spend much of its time in some warm sunny spot, as on a rocky out- 

 crop. In such a place, too, it waits for prey. The cleared area of a trail 

 is often made use of as a sunning place and this accounts for the number 

 of rattlers encountered by hikers. If come upon, on trail or rocks, a rattle- 

 snake may remain quiet, or again it may endeavor to glide away. Only 

 when it is cornered, or when it 'thinks' itself cornered, is the rattler likely 

 to prepare for striking. 



In the winter months rattlesnakes ' ' den up, ' ' that is, go into dormancy 

 in holes in the ground and sometimes in crevices in rocks. In certain 

 places, ground squirrel burrows are used. In a few localities regular dens 

 have been reported where large numbers of these snakes are said to con- 

 gregate together for the winter season. One such den is reported to have 

 been found in the neighborhood of Horseshoe Bend when the Yosemite 

 Valley Railroad was being constructed previous to 1908. Another is said 

 to have been blown up in Hetch Hetchy Valley incidental to work on the 

 San Francisco water project. We have no personal knowledge of occur- 

 rences of this nature. 



Pacific Mud Turtle. Clemmys marmorata (Baird and Girard) 



Field characters. — Body protected by a firm ' ' s-hell, ' ' arched above, flat on under 

 surface; this shell consists of an outer horny integument, divided into numerous plates, 

 and a supporting structure beneath composed of bone. Total length of shell up to 5l^ 

 inches. Upper surface olive brown ; under surface yellow, irregularly marked with black 

 or brown. 



Occurrence. — Kesident in Lower and Upper Sonoran zones on west side of Sierra 

 Nevada. Recorded at Lagrange, Pleasant Valley, and Smith Creek, 6 miles east of 

 Coulterville. Lives in ponds and in the quieter and deeper portions of streams. 



The Pacific Mud Turtle, the only species of native fresh-water turtle 

 to be found in central California, is resident in suitable places in the lower 

 western portion of the Yosemite section. This turtle lives in ponds and 

 in the parts of creeks and rivers which are deep and in which the current 

 is very slow. The site selected for a resting place is usually some rock 

 or log projecting above the surface of the water and at the same time 

 some distance from the shore where there is no danger of surprise by 

 enemies which prowl along the bank. In addition to these precautions 

 against attack, turtles are gifted with rather keen sight, and they can 

 detect an object moving along the shore when it is still some distance away. 

 If a person comes rapidly up to the side of a pool where some turtles are 

 out on their resting places the animals drop at once into the water and 

 seek safety on the bottom; usually they do not return to the surface for 

 some time. In the fall, the turtles disappear and do not come to notice 

 again until the return of warm weather the following spring. 



