The Columbia has cut its gorge into a plateau consisting of many layers of flood basalt, one of the world's great flood basalt provinces. The layering is impressive (and shows how basalt can mimic sedimentary rock, at least when viewed from a distance, which has to make you wonder about the latest speculations on the nature of the Martian surface rock) and in places the basaltic columns are also impressive, though nowhere as good as we would see later in the trip in eastern Washington, Idaho and Montana.
Also of note are the wonderful waterfalls which cascade from the southern wall.
Next: Mount Saint Helens.
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