I’ve been through the “scablands” and Columbia Gorge a few times. It’s hard to get a mental picture of the Missoula floods until you see what’s left of the flood basalt that was in the way.
http://www.iafi.org/floods.html
The above is a link to society for the ice age floods. As you head south to Hanford from Vanatage, when you go south across the river and then up that steep hill, look back to the north and there is a huge ridge (100 feet+ tall?) along the north side of the river that is an old sand bar.
I did a job near the mouth of the Columbia river. It was all basalt rock about 20 feet down, acres of basalt. They drilled down and after 200 feet or so they hit soft sand. (Not sandstone rock!) Not sure how that works!