Where Is The Columbia River Plateau?

The Columbia River Plateau is situated in parts of states of Washington, Idaho and Oregon in the United States of America. It appeared in late Miocene and early Pliocene era and it was one of the largest flood basalts to appear on the surface of the earth with an area of 63,000 square miles or 160,000 square km. It was the consistent flow of lava for approximately 10-15 million years that was accumulated giving the plateau a thickness of 6000 feet. As the molten rock came on the surface, the crust of the earth sank in gradual manner into the space left vacant by the rising lava. The falling of the crust produced a large plain which is now famous as Columbia Plateau or Basin.   

The lava which flowed over the area filled the stream valleys first and which in consequence caused formation of impoundments or lakes.