Watercourses do change considerably, but little rivers like the Witch don't jump bigger ones. Those are some pretty glaring errors.
A few years back, some guys from Independence, Missouri, who were friends of my Great Uncle, located and dug up a Steamboat that sunk on the Missouri River in 1856. It was eighty feet deep in the ground under a Kansas cornfield!
http://en.wikipedia.org/wiki/Arabia_Steamboathttp://1856.com/The story is almost completely unconnected, but still very interesting.
