The Sioux named Medicine Rocks Inyan-oka-la-ka, or "Rock with a Hole in It." Evidence suggests the ancestors of modern-day American Indians lived and hunted in southeastern Montana beginning at the end of the last ice age, about 12,000 years ago, when summers were cooler and large mammals such as woolly mammoths provided a bountiful harvest. As the climate warmed over the next few thousand years, mammoths and other prehistoric mammals became extinct, and American Indians relied on buffalo for food, shelter, clothing and tools. On the prairie around Medicine Rocks, the Northern Cheyenne, Sioux, Gros Ventre, Assiniboine, Crow, Shoshone and Arapaho sought shelter among the sandstone formations and gathered edible and medicinal plants growing in the sandy soil. Artifacts recovered from the park have provided insight into how early people lived and survived on the Plains, helping archaeologists understand how American Indians may have adjusted travel patterns, hunting and gathering methods, and daily routines according to seasonal resources. Petroglyphs engraved in sandstone rock faces advertised personal feats, promoted fertility, marked territories and counted days or seasons; projectile points flaked from stone and fitted to wooden shafts could pierce the hide of a buffalo; potsherds came from clay cookware shaped by hand and baked in fire; and tipi rings were left when rocks that anchored tipi covers formed circles on the windy prairie.