Try the flooding of Lake Missoula and creation of the Columbia Gorge as one reason the Columbia wooly mamoth may have been wiped out. That was one epic (actually several) flood. Sixty MPH, and 200+ feet above current river levels. Boulders so large they were carried to the Oregon Coast Range.
Are you talking about the flood from the break of the ice dam? If you’ve ever been to “dry falls” in WA, they figure that the canyon downstream of dry falls was formed all at once... Maybe a period of three or so DAYS, after the ice dam finally broke.