When I attended Whitman College, I met a wonderful instructor named Dick Clem who awakened the fascination with geology I still feel 40 years later. One thing he showed us on our field trips was the evidence found by J. Harlan Bretz of the great Ice Age floods that sculpted the landscape of what is now eastern Washington.
Ice sheets moving down from Canada had created a huge lake behind the Bitterroot Mountains of Montana. Periodically the ice dam would fail sending a wall of water across the land. The floods plucked out rocks to create the coulees of the channeled scablands and piled the rubble in deposits all over the area. There are even gravel deposits as far downstream as Cowlitz County. Once high-level air photography became available the evidence was incontrovertible.
Later, I took a degree in Geology from the University of Puget Sound and did graduate work at Western; lots more about how glaciers had shaped the landscape of the North West.
Bretz's ideas seemed sound to me since it met the most important qualification of a scientific theory: it enabled one to accurately predict what one was going to find. When I came to Cowlitz County I looked for, and found, deposits of water-rounded pebbles containing kinds of rocks that are not found as bedrock within hundreds of miles of here. They are hundreds of feet above the Columbia River, as Bretz's theory would lead one to expect.