In north-central Montana, pre-Columbian hunters built mile-long stretches of drivelines. They used the drivelines to funnel buffalo herds from fertile grazing patches towards the edge of a steep bluff.
Archaeologists have radiocarbon dated bison bones to between 900 and 1650 CE at two different driveline sites. The majority of kills occurred in the final 250 years of that period.
Evidence suggests that those hunters burned patches of the prairie to spur the growth of fresh grass in the gathering basins to entice herds of ravenous bison. Southern Methodist University archeologist Christopher Roos and his team studied layers of sediment exposed in the riverbed walls of two tributaries of the Two Medicine River.
The team, including members of the Blackfeet Tribe, found between five and eight layers of charcoal residue at each site. It is a sure sign of nearby prairie fires.
They radiocarbon dated them to between 1100 and 1650 CE – the height of the bison jumps. They did not look like the result of natural wildfires, but rather fires that hunters deliberately set.
The fires were most likely spring burns to prepare for fall hunts. Their goal could have been to stimulate new growth to attract bison.
They seemed to have set them in carefully chosen spots. “Burning of this kind in fescue prairies changes the composition of the grasses and forbs,” Roos said.
That means that a hunter-gatherer society with a comparably low population density had an important impact on the environment.