The subspecies of pocket gopher occupying the Puget Sound area are highly restricted in their habitat preference; they occur only on the grassy prairies of the glacial outwash aprons. They do not occur in woods, brush or even small openings on the borders of the prairies. The alpine forms occupy the mountain meadows and are slightly less selective in their habits. It should be noted that in western Washington the forests are far more open at higher altitudes than at low elevations. The races inhabiting the desert are found in open areas, often in sandy places. They occur more rarely in areas where the soil is baked and claylike, and then usually in the vicinity of springs or watercourses. The race _T. t. fuscus_ has a wide range of tolerance as regards environmental factors; it occurs near Wenatchee in essentially desert conditions, in alpine meadows of northeastern Washington, and in many habitats at intermediate elevations. It occurs also in brushy areas and is often abundant in open pine forests. Since the gopher usually has a narrow range of tolerance as regards its environmental adaptations, this has resulted in considerably more isolation than is the case with other mammals, and has probably contributed to the formation of the many subspecies. Within the range of almost every race, microgeographic races, or local populations with distinctive characters, are found. Many subspecies of _Thomomys_ are probably the result of chance fixation of genetic characters already present in a more genetically variable ancestral population, and the loss of other genetic factors. Such races might be considered degenerative (see Dalquest and Scheffer, 1944: 24). [Illustration: FIG. 98. Distribution of the northern pocket gopher in Washington. A. _Thomomys talpoides devexus._ B. _Thomomys talpoides columbianus._ C. _Thomomys talpoides aequalidens._ D. _Thomomys talpoides wallowa._ E. _Thomomys talpoides fuscus._ F. _Thomomys talpoides yakimensis._ G. _Thomomys talpoides shawii._ H. _Thomomys talpoides immunis._ I. _Thomomys talpoides limosus._ J. _Thomomys talpoides douglasii._ K. _Thomomys talpoides pugetensis._ L. _Thomomys talpoides tacomensis._ M. _Thomomys talpoides glacialis._ N. _Thomomys talpoides tumuli._ O. _Thomomys talpoides yelmensis._ P. _Thomomys talpoides couchii._ Q. _Thomomys talpoides melanops._]