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. [Illustration: 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. The Columbia Lava Province includes the land both north and south of the Snake River. Since the Snake River serves as a barrier to some species, it seems better to term the area north of the Snake River the Columbian Plateau Area and that to the south the Southeastern Washington Distributional Area. The Blue Mountains Province and the Blue Mountains Distributional Area are the same. [Illustration: FIG. 5. Yakima Park (or Sunrise Park), elevation 6,000 feet, Mount Rainier, August 29, 1932. (Photo by 116th Photo Section, Washington National Guard, No. 014-36A-116.)] [Illustration: FIG. 6. Columbia River at Hunters Ferry, Stevens County, Washington, April 15, 1940. (Fish and Wildlife Service photo by Victor B. Scheffer. No. 932.)] [Illustration: FIG. 7. Blue Mountains, Umatilla National Forest, Washington, looking north-northeast across Al Williams Ridge to Tucannon River; 1933. (Forest Service photo, No. 4437.)] PHYSIOGRAPHIC PROVINCES DISTRIBUTIONAL AREAS Cascade Mountains { Cascade Mountains { Yakima Valley Puget Sound } Willapa Hills } Western Washington Olympic Mountains } Okanogan Highlands Northeastern Washington Columbia Lava { Columbian Plateau { Southeastern Washington Blue Mountains Blue Mountains CLIMATE AND VEGETATION The life-zone theory of plant and animal distribution was proposed by Merriam (1892). Merriam's life-zones have been severely criticized by many authors, especially because an error was made in computing some of the data on temperature. However, zonation of vegetation and animals is obvious in Washington, and the life-zone concept has been employed in Washington by numerous botanists and zoölogists. Among them are: Piper (1906), Taylor and Shaw (1927), Jones (1936, 1938) and St. John (1937).