More than 12,000 years ago the Missoula Flood, the largest and most powerful scientifically documented freshwater flood to occur on earth, happened in the Pacific Northwest.During a period of several thousand years a single large flood, a few, or possibly as many as 100 of these floods scoured the 600-mile path when the glacial ice dam repeatedly reformed, the lake filled up again, and the ice dam broke again. Each flood was separated by decades or centuries.
Before the flood, the Columbia River valley walls sloped gently down to the river. The powerful flood scoured the landscape of vegetation, removed up to 150 feet of topsoil and deeply eroded its volcanic bedrock on both sides of the river. After the flood, the drastically eroded valley walls ended in very steep vertical slopes. The photo shows an eroded 200’ basalt wall of the Columbia Gorge rising almost vertically. It is located immediately east of the mouth of Oneonta Gorge, beginning east of milepost 34.3.
The 125’ straight bore Oneonta Tunnel (1914), one of four tunnels on the Historic Columbia River Highway, was reopened August 19, 2006. For the first time since it was filled with debris in 1948, daylight could be seen through the tunnel.
Instructions for logging waymark: A photograph is required of you (or your GPS receiver, if you are waymarking solo) and Oneonta basalt wall and tunnel.