Columbia Plateau

This article is about the geographic feature. For the associated ecoregion, see Columbia Plateau (ecoregion).

The Columbia Plateau covers much of the Columbia River Basalt Group, shown in green on this map. The Washington cities of Spokane, Yakima and Pasco, and the Oregon city of Pendleton, lie on the Columbia Plateau.

The Columbia Plateau is a geologic and geographic region that lies across parts of the U.S. states of Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by the Columbia River. In one of various usages, the term "Columbia Basin" refers to more or less the same area as the Columbia Plateau.

Geology

Main article: Columbia River Basalt Group

During late Miocene and early Pliocene times, one of the largest flood basalts ever to appear on the earth's surface engulfed about 63,000 square miles (160,000 km²) of the Pacific Northwest, forming a large igneous province. Over a period of perhaps 10 to 15 million years, lava flow after lava flow poured out, ultimately accumulating to a thickness of more than 6,000 feet (1.8 km). As the molten rock came to the surface, the Earth's crust gradually sank into the space left by the rising lava. The Columbia River Basalt Group consists of seven formations: The Steens Basalt, Imnaha Basalt, Grande Ronde Basalt, Picture Gorge Basalt, Prineville Basalt, Wanapum Basalt, and Saddle Mountains Basalt. Many of these formations are subdivided into formal and informal members and flows.

The subsidence of the crust produced the large plateau—a large, slightly depressed lava plain sometimes also known as the Columbia Basin. The ancient Columbia River was forced into its present course by the northwesterly advancing lava. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. Entities found in these lake beds include fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.

Flora

Part of the Columbia Plateau is associated with the Columbia Plateau ecoregion, part of the 'Nearctic temperate and subtropical grasslands, savannas, and shrublands' ecoregion of the Temperate grasslands, savannas, and shrublands Biome.

Geography

Washington cities in the Columbia Plateau include:

• Davenport
• Reardan
• Kennewick
• Moses Lake
• Pasco
• Pullman
• Richland
• Spokane
• Walla Walla
• Yakima*
• Goldendale
• Deer park

Oregon cities in the Columbia Plateau include:

• Hermiston
• Hood River
• Pendleton
• The Dalles
• Milton-Freewater

See also

• Grand Coulee
• Channeled scablands
• Interior Plateau

External links

• USGS Page on Columbia Plateau
• Geology of Lake Roosevelt National Recreation Area (source of much of this page)
• Guide to digital documents and photographs about the Columbia River area.
• Columbia River Basin Ethnic History Archive