After J.T. Pardee studied the canyon of the Flathead River (100 years ago), he estimated that flood waters in excess of 45 miles per hour would be required to roll the largest of the boulders moved by the flood. He estimated the water flow was 9 cubic miles per hour, more than the combined flow of every river in the world. More recent estimates place the flow rate at ten times the flow of all current rivers combined. The flow from the Missoula Floods was one to ten times the flow rate of all the rivers in the world combined!All caused by global warming at the end of the last Ice Age.
Everybody should ask their climate kook acquaintances about the cause of that.
Are you a fan of Randall Carlson? He has done some great analysis of the Scablands floods and the Bonneville Lake flood that followed the course of the Snake River.