Washington | State Capital, Map, History, Cities, & Facts | Britannica

Relief and drainage

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Washington has seven physiographic regions. In the northwest the Olympic Peninsula borders the Pacific Ocean south of the Strait of Juan de Fuca. Dense rainforests extend along the western slopes of the rugged Olympic Mountains, which rise to 7,965 feet (2,428 meters) on Mount Olympus.

The Willapa Hills parallel the coast from Grays Harbor to the Columbia River in the southwest. Gentle forested slopes descend to an indented Pacific coastline and, north and east of the hills, to the fertile Chehalis and Cowlitz valleys.

The Puget Sound Lowland stretches southward from Canada between the Olympic Mountains and the Cascade Range to join the valleys of the Chehalis and Cowlitz rivers, which form an extension to the Columbia River. Deep waters and fine harbors in Puget Sound, together with relatively flat terrain along its shores, favor the densest population and greatest commercial development in the state.

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The Cascade Range, east of the Puget Sound Lowland, has the state’s highest elevations. Its chain of volcanic peaks includes 14,410-foot (4,392-meter) Mount Rainier, the fifth highest peak in the conterminous United States. Mount St. Helens, located in the Cascades near the Oregon border, erupted violently in 1980 and blasted away its volcanic cone, reducing the mountain’s elevation from 9,677 feet (2,950 meters) to 8,363 feet (2,549 meters). The highest peaks of the Cascades have permanent glaciers.

Occupying most of central Washington, the Columbia basin is surrounded by the Cascades to the west, the Okanogan Highlands to the north, uplands to Idaho to the east, and the Blue Mountains to the southeast. It is a basalt plateau lying at an elevation of about 1,000 to 2,500 feet (300 to 750 meters) and is drained by the Columbia River and its main tributary, the Snake. Glaciation, flooding, and wind have shaped diverse landforms, although the general appearance is that of a large interior plain.

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The Okanogan Highlands, in the northeast, are an extension of the Rocky Mountains. Their north-south ranges, with summits that rise to more than 7,000 feet (2,100 meters), are separated by glaciated trenches. Most of the state’s metallic ores are found in this region.

The Blue Mountains, which extend into Washington from Oregon, consist of uplifted plateaus and ranges in the southeastern corner of the state. Gentle slopes and broad valleys descend from 6,000-foot (1,800-meter) heights to the Columbia basin. Outliers to the west comprise the Horse Heaven Hills and Rattlesnake Hills.