I was thinking about the river last night. Someone had mentioned to the effect of what would happen if an earthquake caused a rock slide that closed off the river. This is certainly possible due to the river here threading it's way through the mountains and into some very narrow spots where the river is not that wide. In the linked video, the canyon walls are only about 120' wide...

That potential 200 millions of water per minute water flow would have to go somewhere and take out the land and highway in lower areas close to the river. This would result in a whole new set of problems as the few areas along here where people live (and where you might may be waiting for potential help/rescue of sorts) would be vulnerable as these areas are typically close to the river. If the river was to be obstructed, seeking very high ground would be a priority. In this case, I would think that the higher the better as that much water is going to cover a lot of low land in a very short time span?