Physical Geography

Washington's physical features range from glacier-covered mountains to broad, sea-level lowlands. Beginning on the coast and moving eastward, the state's natural regions are the Coast Ranges, Puget Sound Basin, Cascade Range, Columbia Plateau, and Rocky Mountains.

The Coast Ranges are mountains extending north and south along the Pacific coast. They are relatively low in southwestern Washington, near the mouth of the Columbia River, but increase in height toward the north and reach their highest point at Mount Olympus (7,954 feet [2,424 m] above sea level) in the Olympic Mountains.

The Puget Sound Basin is situated in northwestern Washington between the Coast Ranges and the Cascade Range. The basin includes Puget Sound, an arm of the Pacific; numerous islands, of which Whidbey is the largest; and the lowlands bordering the sound. The waters of Puget Sound extend southward into Washington for about 100 miles (160 km) and provide many deepwater channels and harbors. The sound is one of the best inland waterways in the world, and is of great economic value. Most of the state's population, commerce, and industry are centered in this area.

The Cascade Range, east of Puget Sound Basin, extends north and south through central Washington. Along the main crest of the Cascade Range are numerous peaks that rise 8,000 feet (2,440 m) above sea level. Towering above these peaks are a number of snowcapped volcanoes. Highest is Mount Rainier, which reaches 14,410 feet (4,392 m). Other volcanic peaks include Mount Adams, Mount Baker, and Mount St. Helens. Mount St. Helens, once thought to be virtually extinct, brought widespread devastation with its violent eruption in 1980.

The Columbia Plateau, east of the Cascades, covers all of eastern Washington except for the extreme northern section. The plateau is a vast, treeless region varying in elevation from 600 to 2,000 feet (180 to 600 m). Features include lava beds, deep coulees (ravines), and, especially in the Palouse region of the southwest, undulating hills. In the extreme southeast rise the Blue Mountains.

The Rocky Mountain section of Washington occupies the northeast and consists of several relatively low ranges, including the Kettle River Range and the Selkirk Mountains.

Washington's coast has many bays and capes and is so irregular that it totals more than 3,100 miles (5,000 km).

The largest river in Washington is the Columbia, which ranks only after the Mississippi and Ohio rivers in volume of water. Major tributaries in Washington are the Snake, Pend Oreille, Spokane, Yakima, Wenatchee, and Okanogan rivers. The Columbia River system supplies large amounts of water for hydroelectric power and irrigation. Hydroelectric power is of particular significance; no state equals Washington in either developed or potential waterpower.

Puget Sound is the largest body of water in the state of Washington. The largest lake is Franklin D. Roosevelt Lake, a reservoir behind Grand Coulee Dam. Other lakes include Lake Chelan and Potholes Reservoir, both in eastern Washington, and Ross Lake, in the Cascade Range.

Washington has two dissimilar climates; the dividing line is the crest of the Cascade Range. To the west the climate is humid and moderate, largely because of the Pacific Ocean. Winds moving inland from the ocean cool the land during summer and warm it in winter. As a result, temperature variations are small, considering the state's northern latitude. Seattle's temperatures, for example, average about 40°F. (4°C.) in January and 66°F. (19°C.) in July.

Precipitation is extremely heavy throughout much of western Washington. Some windward-facing slopes of the Olympic Mountains and Cascade Range receive more than 120 inches (3,050 mm) of precipitation a year. The Puget Sound Basin receives substantially less. Drizzling rain, high humidity, cloudiness, and fog occur during much of the year. Snowfall is heavy in the mountains but light and infrequent along the coast.

The Pacific's influence diminishes rapidly beyond the Cascades' crest, in eastern Washington. The region is also more exposed to hot and cold air masses from the continent's interior. Consequently, winters are colder and summers hotter here than in western Washington. Temperatures in Spokane, for example, average 25°F. (-4°C.) in January and 70°F. (21°C.) in July.

Most of eastern Washington is dry, averaging less than 20 inches (510 mm) of precipitation a year. Part of the Columbia Plateau is virtually semidesert, with only 5 inches (130 mm) of precipitation annually. Snowfall is light except in the high mountains.

Washington's vegetation corresponds generally to its two climatic zones. Dense evergreen forests predominate in western Washington. Found there are such important timber species as Douglas fir, western hemlock, western red cedar, Sitka spruce, and several species of true firs. On the eastern flank of the Cascade Range are sparser forests, chiefly of ponderosa and lodgepole pine, Douglas fir, Engelmann spruce, western larch, and white fir.

Grasses and shrubs—notably bunch grass, sagebrush, and greasewood—grow on the lower and flatter lands east of the Cascades. The mountain ranges are forested.

Large mammals found in Washington include bear, elk, deer, and cougars. Among the smaller mammals are bobcats, martens, foxes, and coyotes. There are many species of fish and birds, including migratory waterfowl.