Geology
The Columbia River Gorge began forming as far back as the Miocene, (roughly 12 - 17 million years ago), and continued to take shape through the Pleistocene, (700,000 - 2 million years ago). During this period the Cascades Range was forming, which slowly moved the Columbia River's delta about 100 miles (160 km) north to its current location.
Although the river slowly eroded the land over this period of time, the most drastic changes took place at the end of the last Ice Age when the Missoula Floods cut the steep, dramatic walls that exist today, flooding the river as high up as Crown Point. This quick erosion left many layers of volcanic rock exposed.
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