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Major Rivers, Columbia River

Rocky Mountain Trench, Rock Island Dam, Grand Coulee Dam, principal river, Columbia Basin

The Columbia River, the principal river of the Pacific Northwest, originates in Canada and flows for 2,000 km (1,240 mi). It occupies a portion of the Rocky Mountain Trench, a huge depression that extends from Montana to the Yukon Territory in Alaska. Its main tributary, the Snake River, drains part of Idaho, Montana, Wyoming, Utah, and Nevada. The Snake joins the Columbia for the riverís lower 480 km (300 mi). The deep valley of the Columbia River forms part of the border between Washington and Oregon, before breaking the north-south trend of the Cascade Mountains and entering the Pacific Ocean.

The river has a steep gradient, descending almost 400 meters (almost 1,300 feet) over its 1,190-km (740-mi) U.S. segment. In addition, it has an annual flow rate of about 8,000 cubic meters per second (about 265,000 cubic feet per second), which is exceeded only by that of the Mississippi and St. Lawrence rivers. As a result, the Columbia possesses the greatest hydroelectric potential of any waterway in North America. A total of 11 dams have been constructed on the river in the states of Washington and Oregon to improve navigation and produce electricity.

The Rock Island Dam built in Washington in 1929 was the first dam built on the river. In the 1930s the Grand Coulee Dam, also in Washington, was completed. As the largest hydroelectric plant in the world, and one of the largest dams in the nation, it impounds water used to irrigate more than 400,000 hectares (more than 1 million acres) of semiarid land in central Washington. Many other dams have been constructed on the tributaries of the Columbia River. Large urban areas in Washington and Oregon use most of the power produced in the Columbia Basin.

Spokane, Washington, is the dominant urban center in the central interior lowland portion of the Columbia Basin. Portland, Oregon, has become the principal commercial center of the Lower Columbia Valley, with modern port facilities at the confluence of the Columbia and Willamette rivers.

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