346 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



that the spring run-off is retarded and the supply to the streams below 

 is distributed over a longer period of time; furthermore, the porous 

 soil retains the water longer than packed ground and gives it up with 

 corresponding slowness. Spring floods are less liable to occur and a 

 more regular water supply is insured to the lowlands. 



(5) A porous, moist soil produces a fuller vegetational cover — 

 forest, brushland and meadow — and this again favors water con- 

 servation. 



(6) The ground is rendered more fertile through the loosening of 

 the soil as well as through the permeation of it by the tunnels them- 

 selves, thereby admitting both air and water to the roots of the 

 plants; the mineral constituents of the soil become more readily 

 available, and the rootlets are better able to penetrate the earth. 



(7) The accumulated vegetational debris on the surface of the 

 ground is eventually buried by the soil brought from below by the 

 gophers, and becomes incorporated to form the humus content so 

 favorable for the successful growth of most kinds of plants. 



My readers will have been reminded by a portion of the above 

 considerations of Darwin's classical study of the relation of earth- 

 worms to soil formation. There is undoubtedly a parallel here, the 

 more significant in that the earthworm is a relatively rare animal in 

 California; and what earthworms are here are of small size and 

 of relative inconsequence in effect upon the soil. The pocket gopher 

 is wonderfully equipped to handle the refractory young soils of the 

 semiarid Sierran slopes, and his role here is, in a way, that of Dar- 

 win's earthworm in England. 



The greatest of all agencies of erosion in the Sierra Nevada, the 

 glaciers, so stressed by John Muir, have now ceased to operate, and 

 the less obvious agencies come into prominence. The element of time 

 granted, we are able to conceive of vast accomplishments on the part 

 of even so humble a contributor as the pocket gopher. Gophers have 

 been at work as gophers of modern type since Miocene times. Prof. 

 Andrew C. Lawson thinks that the Sierran block had not begun 

 to uptilt until early Pliocene. Gophers have probably been at work 

 on at least the lower slopes a good share of the entire time occupied in 

 the uplift of the Sierra Nevada. 



As in the case of Darwin's earthworms, there is plentiful evidence 

 in California as to the function of burrowing rodents in burying 

 large objects, such as rocks and logs. Ground squirrels and pocket 

 gophers both show an inclination toward placing their nesting cham- 

 bers beneath objects that will protect them from being dug out by 

 burrowing enemies, such as badgers and coyotes. The earth is taken 

 out from beneath a rock or a boulder by the rodents and deposited 



