Three spear points found near the ribs of an imperial mammoth in Oklahoma suggest that people lived here at the end of the last Ice Age. Archaeologists believe these nomadic people traveled from one grassy plain to another hunting mammoth and giant bison, and the Kiamichi Valley below provided a travel corridor to and from these hunting grounds. As the climate gradually warmed and dried, long periods of drought and flash floods began to change the landscape. Spruce and pine forests in the Kiamichi Valley were replaced by hardwood trees, and mammoths and giant bison disappeared from the plains. As the climate and landscape changed, people moved into forested areas to find food, hunted smaller game such as deer and elk, and relied on acorns, nuts, berries, and other forest plants as important food sources.