[Free Trapper]

Could the river have changed course even 40-60 miles years back?If so,the old riverbed would leave oxbows that tend to fill in and become marsh and eventually dry land.This can happen quickly under the right conditions.

[TexanToTheCore]

I noticed on the Topo map that the rivers flowing through the area meander quite a bit. This occurs when the gradient is slight and the flow is quite slow. Those oxbows could very well form and become marshes.

[okie01]

"Could the river have changed course even 40-60 miles years back?"

Unlikely. Since Kensington is almost due east of the source of the Red (or Bois de Sioux, at that point).

As you describe, on a flat landscape, rivers will wander all over their flood plain, constantly scouring and depositing, leaving oxbow lakes in their wake. But this close to the source, there would not have been sufficient flowage for such a phenomenon to occur.