Nature
10
About fifteen million years ago, molten stone poured from cracks in the earth near the eastern border of today's Washington and Oregon. Layers of flowing lava spread west, coating 65,000 square miles with andesite and basalt up to two miles thick and pushing the ancient Columbia River north. Then the Cascades rose and erupted. Toward the end of the last Ice Age, an enormous lake in Montana broke through its glacial dam and roared west across the plateau and through the Gorge. This drama was replayed many times, and the water scoured solid rock and topsoil to form scablands, leaving behind giant gravel bars.
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