The topography of the ground moraine exposed by the retreat of the Vashon-Wisconsin glaciers was a barrier to many species of mammals. The rough, rocky surface with thin soil probably first supported mosses and grasses, then brush, and later trees. The earlier stages of plant succession on the deglaciated ground probably presented ideal habitat for yellow pine chipmunks. Certainly the races immediately adjacent to the glaciers extended their ranges farther north than many species. In eastern Washington, _T. a. luteiventris_ spread to the northeastern corner of the state and on into British Columbia. In the northern Cascades, _T. a. affinis_ spread northward and eastward, across the Okanogan River, into northeastern Washington as far as the range of _luteiventris_. The chipmunk of the higher Cascades (_ludibundus_) likewise extended its range northward into British Columbia. In the northwestern Cascades of northern Washington and southern British Columbia, a richly-colored race, _T. a. felix_, now occupies a limited geographic range. This race doubtless originated from _ludibundus_ stock but the method of its development is unknown. Perhaps in early postglacial time, selective factors developed in chipmunks of the western slopes of the Cascade Mountains the rich, dark color of _felix_. The ancestral _ludibundus_ may have given rise to a pale race, _affinis_, in the arid eastern Cascades and a dark race, _felix_, on the humid western slope of the Cascades. This seems improbable for there is no trend to darker color on the western border of the range of _ludibundus_ south of the range of _felix_, and instead, _affinis_ may have given rise to _ludibundus_. A more appealing hypothesis is that a local mutation in some _ludibundus_ stock so changed the range of tolerance of a portion of the population that it was allowed to enter the more dense habitat along the coast north of the Fraser River and, there, isolated by habitat selection, it developed the characters of _felix_. Population pressure later forced it eastward until the eastern border of its range again met the range of the ancestral race, _ludibundus_. The chipmunks of the Olympic Mountains probably reached their present range from the Cascades. Their probable path of emigration was westward from Mt. Rainier, along the glacial outwash train of Nisqualli Glacier, to the moraine and outwash apron of the Vashon Glacier and thence to the Olympics. So similar are the chipmunks of Mt. Rainier and the Olympic Mountains that Howell (1929) included Mt. Rainier in the range of _caurinus_.