Timeframe puts such an event during the near-extent of the last ice age. I grew up 35 miles east of the Mississippi River. For any one else that has driven up and down the Mississippi and Missouri River valleys, the further north and west you go, the broader the valleys gets. What caused the bluffs to rise 500 feet from the valley floors nine miles apart. Sound like a lot of melt water during a very short period to cause that kind of upheaval. In the Upper River Valleys, the bluffs are a ridge parallel to the rivers, not eroded or cut out from erosion like further south.
You've hit upon something that piques my curiosity whenever I think about; that is, around here river bottoms and creek bottoms are much wider than present flows. Erosion? Possible, but I suspect at some point in the past there may have also been enormous water flows from some source. Just a curiosity...