The semicircular limestone cliff at Madison Buffalo Jump State Monument (seven miles south of Logan, 406/994-4042, www.fwp.mt.gov/parks [1], daylight hours, year-round, free for Montana residents, $5 for nonresidents) has changed little since Native Americans regularly drove bison over its edge. In fact, bone shards are still scattered in the dirt at the foot of the cliff, and tepee rings are clustered around the top. Buffalo jumps were commonly used before the introduction of horses; fleet-footed men dressed in skins would lure the bison to the edge of the cliff, then somehow manage to get out of the way as the herd plunged over.
Links:
[1] http://www.fwp.mt.gov/parks