As temperatures rose in the postglacial period, the Great Plains region, a vast belt east of the Rocky Mountains, became grassland, home to huge herds of bison (buffalo). The bison were constantly on the move, followed by hunters for whom they provided the main, though not the only, source of food.
The hunters probably lived in bands of a few families, meeting periodically for activities such as trading and marriages, and especially for communal bison hunts. Large numbers of hunters and helpers made it possible to drive and lure herds into situations where they could be stampeded to their death.
Although the resulting mass kill sites are the best known archaeological remains of the Great Plains Indians, such hunts were probably rare, most kills being of single animals felled by hunters working alone or in pairs to stalk carefully selected individuals - young, old or weak - at chosen hunting sites such as watering places.
The use of bows and arrows from around AD 550 increased the hunters' efficiency, while the introduction of the horse and of guns by Europeans after the 16th century AD ironically improved hunting efficiency so greatly that the bison were almost wiped out within a few centuries.
