The article doesn't really emphasize that glacial Lake Missoula filled and drained multiple times over the years. In the Missoula valley, there are multiple his

The article doesn't really emphasize that glacial Lake Missoula filled and drained multiple times over the years. In the Missoula valley, there are multiple historical beach areas on the mountain sides as a horizontal topo feature. Each one is at a slightly different height. I have a book in storage on this (helpfully titled "Glacial Lake Missoula") -- The craziest statistic that I can remember is that the calculated outflow through one of the canyon choke points was a mile wide, hundreds of feet deep, and travelled at 60mph. There are scars from passing icebergs on the walls.