<P> 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 . </P> <P> During late Miocene and early Pliocene times, a flood basalt engulfed about 63,000 square miles (160,000 km) 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 . </P>

Where is the columbia plateau located on a map