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The Columbia Plateau, also known as the Columbia Basalt Plain, is the prominent geographic feature of the interior Columbia River Basin. The plateau formed between 6 million and 16 million years ago as the result of successive flows of basalt.

Columbia Basin. The Columbia Basin Province occupies the entire south-central portion of the state. It is a wide, arid lowland area between the Okanogan Highlands, the southern Cascade Range, the Idaho Rockies, and continues on through much of eastern Oregon and northern Nevada.

In short, the Columbia River Basin is an essential reason for the Northwest being a dynamic and highly prosperous region within the nation and the world. Hydropower, flood control, irrigation, navigation and recreation are specific benefits that the uniqueness of the Basin and its river system provide.

The Columbia River Basin covers 258,000 square miles and includes parts of seven states and one Canadian province. In its 1,200 mile course to the ocean, the river flows through four mountain ranges and drains more water to the Pacific Ocean than any other river in North or South America.

Interesting Facts Throughout history, the Columbia River basin was a historic area for the fur trade, first railroads, and Oregon Trail settlers. In 1996, a 9,000-year-old skeleton was found along the river in Washington. At 500 feet tall, the river's largest dam is the Grand Coulee Dam.

In a river basin that is mostly mountains and steep valleys, the Columbia Plateau is an area of flat land and gently rolling hills cut by the sometimes steep river canyons of the Columbia and its tributaries. It is a roughly triangular-shaped area about 250 miles on a side.

The Columbia Basin is an arid sagebrush steppe and grassland, surrounded on all sides by areas of higher moisture, predominantly forested, mountainous ecological regions. Habitats within the Blue Mountains ecoregion include desert-like shrubland, grasslands, pine forests and alpine highlands.