We drove across the Columbia River and continued eastward, dropping into Moses Coulee, a canyon with vertical walls of layered basalt. We gathered the students on a small rise and asked them how the canyon had formed. They immediately ruled out wind and glaciers. The valley was not U-shaped like a typical glacial valley, and none of us could imagine how wind might gouge a canyon out of hard basalt. But neither were there rivers or streams. After a while I pointed out that we were standing on ...
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