People have occupied this rugged country for around 12,000 years. During the late Pleistocene age, small bands of nomadic hunters known as Paleo-Indians were attracted to the Caprock escarpment, where they found shelter from harsh winters and resources including plentiful game, drinkable gypsum-free water, and abundant firewood. Between 1000 A.D. and 1541 A.D., groups of American Indians hunted along the Caprock escarpment and established permanent villages to the north along the Canadian River breaks. They developed a close knowledge of bison behavior and hunted by herding bison into box canyons or gullies, or driving them into thick mud where they were killed at close range and butchered on site. The Caprock escarpment itself has been shaped by erosion along the eastern edge of the High Plains for the last 3 million years, as spring and summer thunderstorms sent torrents of water through the area, scouring canyon walls and cutting deeper into bedrock. This ecotone, where the High Plains and Rolling Plains meet, has produced a rugged landscape with great wildlife diversity and habitat for species adapted to rough, rocky terrain.