The Columbia River is the largest river in volume flowing into the Pacific Ocean from North America, and the second largest by volume in North America after the Mississippi. It is also home to several ports which have helped make the river system the United State's largest wheat handler, with ten to 12 million tonnes moved annually, representing 40 per cent of all US wheat exports. The river has its source in British Columbia but is joined by most of its tributaries in the US. By the time it reaches the Pacific near Astoria, Oregon it has travelled 1,232 miles (2,044 km) and drained 258,000 miles~2 (415,211km~2) of land, resulting in a mean total flow rate of 166,000ft~3 (4,700m~3) per second.
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