re: This has always been one of my favorite geologic events.
It was very probably multi floods (60?) and there very probably where people in the path of these floods.
An other place to look for information is IAFI
I agree with you on them being amazing sights. Everytime I visit Western Montana, Eastern Washington or Portland I'm amazed at the amount of water that passed that way. The Dry Falls in the middle of Washington are bigger across and deeper that Niagara Falls and had torn from them boulders the size of cars and houses carried miles away to Ephrata.