Scapanus orarius.—This species probably had a history similar to that of townsendii up to the late Pleistocene. It seems slightly more adaptable than townsendii, and to be able to extend higher into the mountains. The distribution of the subspecies orarius is almost exactly that of S. townsendii. In Oregon, orarius extended eastward over the Cascades where the subspecies schefferi developed. Perhaps this subspecies developed since the Pleistocene and since that time extended along the Columbia River Valley to southeastern Washington. The race yakimensis, in the Yakima Valley area, is closely related to schefferi, and seemingly could have been developed from a stock of schefferi that migrated westward across the Simcoe Bridge.
Neurotrichus gibbsii.—The history of Neurotrichus in North America was probably similar to that of the two species of Scapanus. It tolerates environmental differences to about the same degree that Scapanus orarius does but occurs much farther south (Monterey County, California) than S. orarius. This may be because Neurotrichus has no counterpart to compete with it in the south, whereas Scapanus orarius must compete in northern California with the morphologically similar Scapanus latimanus. S. orarius stops short at this place and S. latimanus occupies all the territory to the south.
The shrew-mole of the lowland of Washington (N. g. minor) probably became distinct from the mountain subspecies (gibbsii) in Vashon-Wisconsin time.
Sorex cinereus.—It is reasonable to suppose that the cinereous shrew had a continuous range across the forested area of British Columbia in pre-Wisconsin time. Without having been isolated, the dark coastal race (streatori) may have developed from the wider-ranging inland cinereus, as a response to the denser, humid, coastal forest-habitat, after having been forced southward to Washington by the Vashon Glaciation. Since that time it is presumed to have reoccupied the coast of British Columbia and southern Alaska. This coastal race might have developed in Vashon time, while isolated in southwestern Washington. The Cascades are populated by a race of the Rocky Mountain Fauna, S. c. cinereus, which probably entered the Cascades from northeastern Washington or British Columbia in Recent Time. The absence of the species in western Oregon, its rarity in western Washington, and its abundance farther north suggest a northern origin and northward rather than southward postglacial movement. Had the full species cinereus been a preglacial resident of western Washington we would expect streatori or a race related to it to occur in the Cascades.
Sorex merriami.—The periphery of the range of this member of the Great Basin Fauna may have been in southeastern Washington since pre-Wisconsin time.
Sorex trowbridgii.—This shrew is a typical Pacific coastal species with an extensive range along the Pacific Coast south of Washington. The Washington population may have been isolated in southwestern Washington during Vashon time or may have crossed the Columbia into Washington from western Oregon early in the Recent. Since the retreat of the ice it has extended northward to southern British Columbia and eastward to the eastern side of the Cascades. Save for crossing the Cascades its postglacial movements have been slight, as is typical of Pacific Coastal species. The race destructioni probably has been isolated on Destruction Island for several thousand years.
Sorex vagrans.—This species probably has had a continuous range over the western United States since the late Pleistocene. The dark coastal race (vagrans) probably was differentiated from the paler races of the Great Basin in response to the more humid climate along the coast.
Sorex obscurus.—The history of this shrew of alpine predilection probably corresponded closely to that of Sorex cinereus. The derivation of the dark, long-tailed, coastal race (S. o. setosus) from the smaller, paler, inland race (obscurus) probably occurred before Vashon-Wisconsin Time. Sorex o. setosus is one of a complex of races distributed along the Pacific Coast from Alaska to California.
Sorex palustris.—This species has a wide range in North America and extends southward in the Cascade-Sierra Nevada Chain to southern California. Its extensive range at present in this mountain chain suggests that it was resident in the Cascades previous to Wisconsin time. Mountain water shrews probably reached the Olympic Mountains from the Cascades by way of the Puget Bridge in early Recent Time.
Sorex bendirii.—This Pacific Coastal species probably had a history very similar to that of Neurotrichus and Scapanus orarius.