The Scablands of eastern Washington began as flood basalts, part of the great Columbia plateau. Basically, they're fairly similar to a mare area on the moon. Then a series of great floods, caused by the repeated building and breaking of glacial dams in Lake Columbia, scoured huge channels across the basalt. The biggest channels, caused by enormous retreating waterfalls, are called coulees. The largest of these, the Grand Coulee, was built by Dry Falls, in its time the largest known waterfall on earth, but now dry. The lower Grand Coulee is now a canyon, partially filled with water, and the upper Grand Coulee is dammed as an overflow irrigation reservoir.
Next: Yoho, Northern Banff, and Jasper.
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