As the flood plain in the Columbia Basin continued to tilt, the Columbia River was forced eastward and joined the Salmon-Clearwater River about six million years ago. About 2.5 million years ago, the Snake River was forced northward by the Blue Mountain uplift and was captured by the Salmon-Clearwater River near the Idaho-Oregon border.

Missoula floods

thumbThe Wallula Gap was widened about the 14th

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