I've always been fascinated by the formation and disappearance of oxbows and oxbow lakes. Once you know what to look for, you can see the remnants of old ones whenever you fly over a river in relatively flat terrain. The meandering path of a slow-moving river explains how sunken riverboats can be discovered miles away from a current riverbed.
Radical Cartography (a site that looks worth exploring, BTW) has reproduced the color illustrations of a 1944 book, The Alluvial Valley of the Lower Mississippi River. Above are a two of the illustrations, showing how complex the stratified geography can be in such a region.