344 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



so far as we know, even at the highest altitudes. There is good evi- 

 dence of the continued work of gophers there, beneath the snow, 

 however deep this may become. During the winter and spring in the 

 high country, where the snow lies deep, they are led to adopt a some- 

 what different method in extending their tunnel systems than during 

 the summer months. The tunnels are then made in the snow itself, 

 a greater or less distance above, and in most of their courses more or 

 less parallel with, the surface of the ground. These snow tunnels are 

 usually greater in diameter than the subterranean runs, perhaps be- 

 cause of the loose texture of the snow as compared with that of the 

 soil beneath ; they serve the purpose of allowing the gophers to reach 

 plants which are embedded in the snow. Many of them are used also 

 in extending the subterranean systems. The earth from below ground 

 is carried up and packed in the snow tunnels previously dug, thereby 

 forming solid earth cores above the level of the ground. When the 

 snow melts in the spring, these cores are lowered intact onto the sur- 

 face of the ground, where they often remain more or less recognizable 

 for several months, despite the winds and summer thundershowers. 



The height to which the snow tunnels extend above the ground 

 depends upon the depth of the snow-fall; but there is reason to 

 believe that their general course is modified by the position of the 

 above-ground vegetation encountered. After the snow has gone, in 

 early spring, we have found portions of earth cores lying on top of 

 flattened branches of snowbush, on fallen tree branches, on logs and 

 rocks, indicating that the animals had pursued courses in the snow 

 well above these objects. When active right after a light fall of 

 snow, the gophers run their tunnels directly upon the surface of the 

 ground, appropriating to their uses as they go the stems of grasses 

 and other plants. 



Very often the earth composing both the winter cores and the 

 summer mounds is quite different in appearance from that of the 

 superficial layer of the ground immediately underneath them. This 

 makes such " workings " very conspicuous, as they are, with reference 

 to the ground on which thej^ lie, in the relation of a geological un- 

 conformity. 



Rather than being a drawback to the interests of the pocket gopher, 

 the snow seems to be of real benefit. Two factors are here involved. 

 I have referred to the timidity of the animal, and this is doubtless 

 due to the relentless pursuit of it by certain carnivorous mammals 

 and birds with the resultant precautions necessary on the part of 

 the gopher to keep out of sight and reach. The snow provides cover 

 which conceals the rodent effectually from certain of its enemies. At 

 the same time, the vertical range of accessible food sources is greatly 



