At least some mammoths appear to have been bogged down in a swamp when dispatched by early hunters. Probably many were lame, or otherwise disabled. Like many other predators, early hunters were essentially culling the herd by working as opportunistic scavengers.

Bullalo jumps are fairly common on the plains of North America, although I can't recall any specifically in Kansas. What you want is a cliff that appears unexpectedly as you are moving the herd along.