The region stretching from northern Colorado to southern Alberta and from the Rockies to the western Dakotas is the land of the Cheyenne and the Blackfeet, the Crow and the Sioux. Its grasslands and river valleys have nurtured human cultures for thousands of years. On cave walls, glacial boulders, and riverside cliffs, Native people recorded their ceremonies, vision quests, battles, and daily activities in the petroglyphs and pictographs they created on stone surfaces. Some sites were clearly intended for communal use; others clearly mark the occurrence of a private spiritual encounter. Elders often used rock art, such as complex depictions of hunting, to teach traditional knowledge and skills. Other sites document the medicine powers and brave deeds of famous warriors.