The state comprises three major geographic zones. In the east, most of interior Washington is made up of the Columbia Plateau and the valleys of the Columbia River and its tributaries. Central Washington is dominated, and the state is divided, by the north-south Cascade Range. To the west of the Cascades lie coastal lowlands in the Puget Trough, Puget Sound and its many arms, and to their west the Coast Ranges, which in part form the backbone of the Olympic Peninsula.The Interior
Washington's interior is a region of hard volcanic substructure, in many places scoured by glacial and river action, that is left largely dry by the shield the Cascades form against the Pacific winds; in some areas, as in the southeastern Palouse hills, loess deposits provide a basis for irrigated agriculture. The Blue Mts., an offshoot of the Rockies in the state's southeast corner, are one of the interior's few forested sections. The Columbia River enters the state from British Columbia in the northeast. After receiving the Spokane River from the east, it turns westward across the state and swings south at the foot of the Cascades, enclosing the Big Bend country. Near Washington's southern border, it receives the Yakima (from the west) and Snake (from the east), then bends westward again, forming the boundary with Oregon as it cuts through the Cascades on its way to the sea.
Washington's boldest physiographic feature is the lofty Cascade Range, rising to 14,410 ft (4,392 m) at Mt. Rainier. The Cascades block the eastward movement of warm ocean air from the Alaska Current, causing abundant rainfall to the west and semiarid conditions to the east. The valleys of the Wenatchee, Yakima, and other rivers flowing eastward from the mountains are important irrigated farming areas, while the Cascades themselves are the site of North Cascades and Mount Rainier national parks, Mount St. Helens National Volcanic Monument, several national forests, and noted ski resorts. Their scenery is a major tourist attraction. Mount St. Helens, on the west slope near the Oregon boundary, is the most recent (1980) Cascade peak to erupt.
Washington's coastal region is one of the wettest areas in the United States, receiving up to 150 in. (381 cm) of rain per year at high elevations; it is correspondingly heavily forested, especially with spruce, fir, cedar, and hemlock. Between the Cascades and the much lower Coast Ranges to the west lies the Puget Trough, a lowland heavily indented by Puget Sound, the site of Seattle, Tacoma, Everett, and most of the state's population and industry. The Coast Ranges rise to 7,965 ft (2,428 m) at Mt. Olympus in the Olympic Mts., within Olympic National Park. Along the Pacific coast, in the southwest, they are breached by two substantial bays, Grays Harbor and Willapa Bay. Puget Sound is filled with more than 300 islands, including the San Juan Archipelago and Whidbey Island; it is entered from the northwest through the Juan de Fuca Strait, from the north through the Strait of Georgia. Point Roberts, the northwesternmost portion of Washington on the latter strait, is the southern end of a peninsula that begins in Canada, and the area is not connected by land with the rest of the state.
Visitors are attracted to Mount Rainier National Park, Olympic National Park, North Cascades National Park, Fort Vancouver and Whitman Mission national historic sites, and Lake Roosevelt National Recreation Area (see National Parks and Monuments, table). Mt. Saint Helens, which erupted in 1980, is now a national monument. Miles of apple and cherry orchards in the irrigated area just east of the Cascades create the spring landscape for which the state is famous. The rugged mountain slopes and grandeur of the Cascades draw climbers during the summer months, and in winter excellent snowfields near Seattle and Tacoma attract skiers. Olympia is the capital; Seattle, Spokane, and Tacoma are the largest cities.