RODENTS IN SOIL FOKMATION GRINNELL 345 



increased ; for the gopher is able to reach plant stems and leaves en- 

 veloped in the snow mantle, many inches and even feet above the 

 ground surface. All this is subject to confirmation through study of 

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



Some estimates made by us while carrying on field work near Por- 

 cupine Flat, Yosemite Park, will serve to indicate the amount of 

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

 of earth put up in the form of winter cores was, on a selected area, 

 1.64 pounds per square yard. Assuming that, on the average, gopher 

 workings covered only one-tenth per cent of the land surface, there 

 would be 3.6 tons of earth put up per square mile, or 4,132 tons over 

 the whole park. This is for 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 can not work. On the other hand, in favorable 

 localities workings occur on every square yard of surface ; so that it is 

 believed that the average of one-tenth per cent is conservative for 

 the park as a whole. In summer the amount of material excavated 

 is probably at least as great as that in winter — exactly how much has 

 not yet been determined. For the year, Mr. Storer and myself feel 

 safe in doubling the total figure just given, which, in another unit of 

 measure, would be close to 160 carloads of 50 tons each. We estimate 

 further that the earth to the above amount is lifted by the gophers 

 an average distance of about 8 inches; 5,500 foot-tons of energy 

 are expended by these little animals in Yosemite Park during a single 

 year. 



The question then presents itself as to the general effect of all this 

 work upon the terrain at large, and further upon the vegetation and 

 even upon the animal life of the region. I will proceed to enumerate 

 some of these relations which seem to be borne by pocket gophers to 

 their environment. 



(1) The weathering of the substratum is hastened by the burrow 

 systems carrying the air and the water and contained solvents to the 

 subsoil particles and rock masses below. 



(2) The subsoil is comminuted and brought to the surface where 

 it is exposed to further, and increased rate of, weathering. 



(3) The loose earth brought up and piled on the surface of the 

 ground thereby becomes available for transportation by wind and 

 water ; rain and melted snow carry it from the slopes down to fill up 

 glacial depressions and to make meadows of them ; and when these are 

 full, the sediment is carried on still farther by the gathering streams 

 to contribute to the upbuilding of the great and fertile valleys beyond 

 the foothills. 



(4) Water is conserved for the reason that snow melts more 

 slowly on porous ground than on hard-packed soil or bare rock, so 



