By John Eliot Allen
The formation of the Grand Coulee remained a secret for a few years, until eventually J Harlen Bretz proved that the Columbia River basin was once the positioning of massive floods 15,000 years in the past that created the panorama we see this present day.
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Extra info for Cataclysms on the Columbia: a layman's guide to the features produced by the catastrophic Bretz floods in the Pacific Northwest
Again the composition was wrong, and there were no craters to suggest meteoric impact. Could mud slides have moved them? No, not from the Rockies to the Columbia Basin, to the Willamette Valley and on to the Pacific! Could glaciers have pushed or carried them? Not here, not so far south. Could humans have moved them? Most unlikely! Even if there had been Indian tribes in the area at the time the rocks arrived in the Gorge, it is inconceivable that Pleistocene humans could have moved them such distances, and certainly there was no logical pattern to their distribution.
And at the ocean such channels come and go with the tides wherever a small stream crosses the beach on its way to the sea. Each rising tide blurs the pattern; but when the ocean retreats, the stream once again cuts and braids new paths over and through the sand. It's a simple matter of water seeking its way over fresh terrain. In fact, those with an experimental bent can create their own Channeled Scabland at home (and at virtually no cost). Lay a garden hose on a flat stretch of dirt and turn it on, a shade above a trickle.
It seemed clear to him, as it had to others,* that vast amounts of water had once flowed through the Basin and out over the western end. But it was puzzling to find the upper lip of the cataract over 200 meters (600 feet) above the level of the present-day river. And the potholes themselveslarge pit-like depressions lying beyond the fallswere of a size beyond anything known elsewhere: hundreds of feet across, much longer than they were wide, and deeper than a house is tall. Now what did all this mean?