From Wikipedia, the free encyclopedia
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.[1] It is a wide flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by the Columbia River. In one of its various usages, the term "Columbia Basin" refers to more or less the same area as the Columbia Plateau.[2]
Geology
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.[3] Over a period of perhaps 10 to 15 million years lava flow after lava flow poured out, eventually accumulating to a thickness of more than 6,000 feet (1.8 km).[3] As the molten rock came to the surface, the Earth's crust gradually sank into the space left by the rising lava.[3]
The subsidence of the crust produced the large plateau - a large, slightly depressed lava plain sometimes also known as the Columbia Basin.[3] 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.[3] Entities that have been found in these lake beds are fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.[3]
Geography
The Washington cities in the Columbia Plateau include:
Oregon cities in the Columbia Plateau include:
See also
References
External links
Coordinates: 45°59′58″N 119°00′05″W / 45.99944°N 119.00139°W / 45.99944; -119.00139
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