Evidence from the Agate Basin site in eastern Wyoming, for example, indicates that humans lived in the Plains at least as early as 8500 B. Radiocarbon dating of material from the Lewisville site near Dallas, Texas, suggests Indians and their precursors may have been in the Plains for at least 38,000 years.
The oral histories of some tribes refer to long-extinct mammoths and other megafauna.
Such migrations accelerated after 1700, as some groups left the Plains and others entered the region.
The Mandans, Hidatsas, and Arikaras traded with peoples from what is today the American Southwest and with more nomadic Plains hunters like the Crows, Assiniboines, Plains Crees, Cheyennes, Arapahos, Kiowas, and Comanches.
Both material goods (agricultural products, dried meat, flint, and animal hides) and cultural products (songs and dances) traded hands.
"Star charts" suggest that the Lakota Sioux have associated parts of the Black Hills in South Dakota with astrometrical phenomena since ancient times.
Some scholars assert that the Sioux peoples originated in the Great Lakes region and only began moving onto the Plains in the late seventeenth and early eighteenth centuries.
Species adapted to the wetter world–such as mammoths, camels, and horses–died out, opening ecological niches in the Plains grassland.
Most of these niches were filled by bison, which were becoming smaller and more mobile in order to be more effective in the drier climate. Around the time that the larger game disappeared, nomadic hunters shifted from Clovis-style spear points and arrowheads to the smaller Folsom points and heads, which were used until about 8000 b.c.While the rise of sedentary villages and agriculture stood out as a key way that Plains peoples adapted to and shaped their environment, migration played an equally important role in the lives of many Indians.It seems that Plains societies were both amalgamating and splitting apart, and that mobility constituted a common response to both social and environmental factors.Through these adaptive strategies, the Plains peoples worked to protect and enhance their political power and their ability to sustain themselves economically, and to maintain their cultural distinctiveness.Although some peoples came to the Plains earlier than others, Native Americans have lived there for a long time.Plains hunters used buffalo jumps like the Head-Smashed-In site in southwestern Alberta as early as 5,500 years ago.