140 ANIMAL LIFE IN THE TOSEMITE 



over logs and rocks, these various locations indicating that the animals 

 had pursued courses through the snow well above these objects, that is to 

 say, at least 12 inches from the top of the ground. When active right after 

 a light fall of snow, the gophers run their tunnels along directly upon the 

 surface of the ground, appropriating to their uses the stems of grass and 

 the other plants encountered as they go. 



Very often the material composing the cores is quite different in 

 character from that of the top of the ground immediately underneath them. 

 This makes the cores very conspicuous, for they are, with reference to the 

 ground on which they lie, in the relation of a geological unconformity. 

 This kind of gopher work is carried on even after but light snow storms 

 in the fall when snow may lie on the ground only a few days. "We noted 

 evidences of such work in 1915, about Tuolumne Meadows after a light 

 snowfall on September 24 and 25, and after another in Yosemite Valley on 

 November 12. 



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

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

 We have referred to the timidity of the animals because doubtless of 

 relentless pursuit by certain carnivorous birds and mammals, and to the 

 resulting precautions evinced by the gophers in keeping out of sight. The 

 snow provides cover which conceals them still more effectually from their 

 enemies. At the same time, the vertical range of accessible food sources 

 is greatly increased, for the gophers are able to reach plant stems and 

 leaves enveloped in the snow mantle many inches and even feet above the 

 ground surface. All this is subject to indubitable proof through study 

 of winter workings uncovered at the time of the spring thaw. 



Some estimates made by our field party while near Porcupine Flat 

 during the first week of July, 1915, will serve to indicate the amount of 

 work done by gophers. It was found that the average amount of earth 

 pushed up in the form of winter cores was, on a selected area, 1.64 pounds 

 per square yard (0.90 kilograms per square meter). Assuming that, on 

 the average, gopher workings cover 0.1 per cent of the Iflnd surface of 

 the Park there would be 3.675 tons of earth accumulated per square mile 

 or 4132 tons over the whole Park. And this in a single winter ! It will be 

 recalled that there are many square miles of either solid rock or slide rock 

 in the Park, where gophers cannot work. On the other hand, in favorable 

 localities workings sometimes occur on every square yard of surface; the 

 average of 0.1 per cent is therefore believed to be conservative for the 

 Park as a whole. In summer the amount of material excavated is probably 

 at least as great as it is in winter — exactly how much has not yet been 

 determined. But for the year we feel safe in doubling the total figure 

 just given, which, 1o put it in another unit of measure, would be close to 



