The range of _Tamias amoenus luteiventris_ in Washington, Idaho and Montana is most unusual (See Howell, 1929; Davis, 1939). From a compact range in Montana, two long fingers reach northward and westward. The western finger crosses Idaho to end in the Blue Mountains of Oregon and Washington. The northern finger crosses northern Idaho, northeastern Washington and extends on into southern British Columbia. Between these two fingers of the range of _luteiventris_ another race (_canicaudus_) is found. This race occupies a more lowland area than does _luteiventris_. The range of _luteiventris_ in the northern Rocky Mountains is extensive. Presumably this race occupied an area farther north in pre-Wisconsin Time and was forced southward to its present range by the Wisconsin glaciers. The original population occupying extreme eastern Washington and adjacent Idaho was _Tamias amoenus canicaudus_. The pre-Wisconsin range of this race might have been more extensive. At any rate, _luteiventris_ which was driven southward displaced _canicaudus_, or some other race of chipmunk, from much of the Rocky Mountains south of the glacier. The northern chipmunks were adapted to more boreal conditions and perhaps otherwise better suited to environmental conditions of the northern Rocky Mountains. A small population of the older established race (_canicaudus_) persisted in lowland areas of eastern Washington and adjacent Idaho. Regarding the range of _canicaudus_, surrounded by the range of _luteiventris_ on three sides and faced by desert on the west, Davis (1939: 220) writes, "It may be that, of these two races, _luteiventris_ has a greater range of tolerance to environmental conditions and, thus, is able to succeed in areas to which _canicaudus_ is not adapted. This inference is supported by the fact that _luteiventris_ occupies a large range which is diversified geographically and climatically, whereas _canicaudus_ seems to be limited to a much smaller, more nearly uniform area." Seemingly _canicaudus_ now exists only in an area ideally suited to it, and one where it can successfully compete with the generally more adaptable and successful _luteiventris_. The maximum extent of the glacial ice, then, found _luteiventris_ the dominant chipmunk in the northern Rocky Mountains, with an isolated population of _canicaudus_ in eastern Washington and adjacent Idaho.