Fig. 3. Mammalian distributional areas of Washington. A. Western Washington. B. Cascade Mountains. C. Northeastern Washington. D. Blue Mountains. E. Southeastern Washington. F. Yakima Valley. G. Columbian Plateau.
The Cascade Mountains Province of [Culver] includes the Yakima Valley Area. This province contains two completely different mammalian distributional areas. The higher mountains possess a boreal, alpine fauna; the Cascade Range itself is called the Cascade Area in this report. The Yakima Valley Area possesses a desert fauna derived from the desert of eastern Oregon.
The land west of the Cascades is separated into three physiographic provinces, the Puget Sound, Willapa Hills, and Olympic Mountains Province. The differences between the mammalian faunas of the Puget Sound and Willapa Hills provinces are slight. The Olympic Mountains possess a few species not found in the lower areas. The similarities of the faunas of the three provinces far outnumber their differences, and it seems best to consider them subdivisions of one distributional area.
Fig. 4. Cascade Mountains in Chelan National Forest, looking southwest at Straight Ridge; Cataract Creek (Methow watershed) at left. (Forest Service photo. No. 4260.)
The Okanogan Highland Province extends, from a physiographic point of view, west of the Okanogan River Valley. This valley, however, is a fairly efficient barrier to mammals. Thus the part of the state east of the Okanogan Valley and north of the east-west flow of the Spokane and Columbia rivers may be called the Northeastern Washington Distributional Area.