POCKET GOPEEBS 



139 



The pocket gopher is one of several Sierran rodents which carry on 

 active existence throughout the entire year. It does not hibernate, so far 

 as we know, even at the highest altitudes. As described beyond, there is 

 good evidence of their continued work beneath the snow, however deep this 

 may become. Yet there is some variation in degree of activity with the 

 change of seasons and at different elevations. In the foothills and lower 

 valleys the rains seem to have much to do with the behavior of these 

 animals. Soon after the first soaking rain of the autumn, and with the 

 first appearance of the annual vegetation, new outpushings of moist earth 

 become conspicuous. In the higher mountains greatest activity, save for 

 that in winter, is shown in September and October. Least surface work 

 is shown during the first few weeks of spring after the snow melts. 



Fig. 24. Cross-section of Sierra Nevada through the Yosemite region showing zonal 

 and altitudinal ranges of Pocket Gophers (genus Thomomys). 



During the winter and spring in the high country, where snow lies on 

 the ground for several months, gophers are, as just stated, continually 

 active, but are led to adopt a somewhat different method in extending their 

 tunnel systems than that used during the summer months. Tunnels are 

 made in the snow some distance above and more or less parallel to the 

 surface of the ground; these "snow tunnels" are usually greater in 

 diameter than the subterranean ones and obviously serve the purpose of 

 allowing the gophers to reach food plants which are imbedded in the 

 snow. Certainly many of these snow tunnels are also used in extending 

 the subterranean system; the earth from below ground is carried up and 

 packed into the snow and thereby solid earth-cores are formed above the 

 ground. When the snow melts these cores are lowered intact onto the 

 surface of the ground, where they often remain distinguishable for several 

 months despite the summer thunder showers. (See pi. 30.) The height 

 to which the snow tunnels extend above the ground depends upon the 

 depth of the snowfall ; but there is reason to believe that their course is 

 also modified by the position of the vegetation encountered. In early 

 spring, after the snow has gone, we have found portions of earth-cores 

 lying on top of flattened branches of snow-bushes, over fallen tree branches. 



