The offset in range of rufa seems best explained by assuming that all of western Washington was once occupied by mountain beavers (rufa) that spread from the Cascades of Oregon to the Cascades of Washington and thence to the western Washington lowlands. This must have occurred early in the interglacial cycle preceding the Vashon Glaciation. While confined to the southern Cascades, rainieri developed the larger size that now separates it from the ancestral rufa that occurs to the west and south of it.
Zapus princeps.—The coastal race of the jumping mouse was probably distinct from the more inland population before Vashon-Wisconsin Times. The differences between them were probably accentuated while the Vashon-Wisconsin glaciers separated their ranges. The western race (trinotatus) was isolated in the southern Cascades and southwestern Washington. After the retreat of the glaciers, trinotatus moved northward through western Washington and the Cascades into British Columbia. The race kootenayensis of the adjacent Rocky Mountains moved eastward through northeastern Washington to the Cascades. The race oregonus, found in the Blue Mountains, has probably been resident there since it evolved from the populations to the east.
Erethizon dorsatum.—I have inadequate basis for speculation concerning the historical distribution of the porcupine.
Ochotona princeps.—The descent of the Wisconsin ice separated the western pikas into two populations. One was confined to the Cascade-Sierra Nevada system and another to the Rocky Mountains. Two races are now found in the Cascades of Washington. One, brunnescens, inhabits the higher Cascades and another, fenisex, the eastern edge of the Cascades. The range of brunnescens extends southward into Oregon while the range of fenisex extends farther north in British Columbia than does that of brunnescens. The principal difference between the two races is the smaller size and paler color of fenisex. In Washington, fenisex occupies a slightly more arid habitat than brunnescens. Further, fenisex lives in talus principally of basaltic rock while brunnescens lives in talus of granitic rock. The basaltic talus is more finely fractured, offering smaller crevices in which pikas can conceal themselves. The granitic rock, on the other hand, forms talus composed of fragments of large size. Freshly fractured granite is pale, whitish gray. After weathering, however, it becomes blackish as the more soluble, pale feldspars are removed, leaving the black hornblend and biotite exposed. Freshly fractured Columbian basalt is blackish but, after weathering, becomes rusty, reddish brown.
In Washington the two races maintain their distinctiveness because selective factors in the basalt talus of the eastern Cascades favor the smaller size and paler color of fenisex while in the higher Cascades, selective factors in the granitic batholith favor larger size and darker color.
The present range of brunnescens in Oregon indicates that this race was the pre-Wisconsin resident of the Cascades of at least southern Washington. Probably fenisex evolved in the arid interior of British Columbia. In color fenisex is intermediate between the dark brunnescens and the pale cuppes of the western spurs of the Rocky Mountains. Probably fenisex was forced southward into the eastern Cascades by the Wisconsin ice and inhabited the area east of the range of brunnescens. This eastern area was not occupied by brunnescens because the basaltic talus was of small size. After the retreat of the ice, fenisex (adapted to more arid habitat than brunnescens), spread northward to the relatively dry valleys of the interior of British Columbia.
The distinctness of brunnescens and fenisex is maintained by selective factors of the habitats they occupy but the zone of intergradation between the two is broad. A tendency towards paleness is noticeable in specimens from as far west as the eastern side of Mount Rainier.
The pikas in the Rocky Mountain area have given rise to a number of races. The pale, small race of northern Idaho, cuppes, entered northeastern Washington with other members of the Great Basin Fauna after the retreat of the ice.
Lepus townsendii.—The white-tailed jack rabbit has probably lived on the Columbian Plateau ever since or even before the time when the Wisconsin ice bordered the plateau on the north.