  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.floyd, ben, et al. "glossary". (1998) hanford reach protection and management program interim action plan. prosser, washington: benton county planning department. == geology ==  during late miocene and early pliocene times, one of the largest flood basalts ever to appear on the earth's surface engulfed about  of the pacific northwest, forming a large igneous province.description: columbia plateau columbia river basalt. united states geological survey, accessed october 9, 2007. 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&nbsp;km). as the molten rock came to the surface, the earth's crust gradually sank into the space left by the rising lava. the subsidence of the crust produced the large plateauâa 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, was
Columbia_River Landforms_of_Hood_River_County,_Oregon Landforms_of_Idaho Landforms_of_Oregon Landforms_of_Umatilla_County,_Oregon Landforms_of_Wasco_County,_Oregon Landforms_of_Washington_(state) Large_igneous_provinces Miocene_volcanism Physiographic_provinces Plateaus_of_the_United_States Pliocene_volcanism Regions_of_Oregon Regions_of_Washington_(state) Volcanism_of_Washington_(state)