The object of communal bison drives was to stampede a herd into a trap where many would be killed, either by falling over a cliff or by being trampled by the animals behind, and where the survivors could be picked off by hunters safely ensconced on the sidelines.
Such traps included both natural enclosures and man-made corrals of logs and stones, as well as steep cliffs. Head-Smashed-In in Alberta, Canada, was one such site, a sandstone cliff whose excellence for the purpose is attested by its long period of use, from about 5400 BC onwards.
At the time of European contact, these techniques were still in use, as eyewitness Fred Hans recounts:
