Columbia Plateau

The Columbia Plateau is an important 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.

During late Miocene and early Pliocene times, a flood basalt engulfed about 63,000 square miles (160,000 km2) of the Pacific Northwest, forming a large igneous province.

The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes.

[2] Evidence suggests that some concentrated heat source is melting rock beneath the Columbia Plateau Province at the base of the lithosphere (the layer of crust and upper mantle that forms Earth's moving tectonic plates).

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.