This is the first time I have seen it suggested that Ice Age flooding carved the Grand Canyon. There were an estimated eleven such floods on the Columbia River which caused many unusual phenomena, but no one has attributed the major valleys of that river to those floods. Being considerably further south, I doubt such floods have anything significant to do with the magnificance of the Grand Canyon.

At the very least a reference to a proponent of such a hypothesis ought to be provided.

(I note that Ethan never responds to comments on his articles in Medium. Perhaps another reader can help here.)