Proto-Indians first arrived in Montana from Asia about 10,000–15,000 years ago. After crossing the Bering Sea causeway, they traveled along the Great North Trail, the rift that opened up along the east face of the Rocky Mountains when the ice fields of the last ice age retreated into the mountains.

These people hunted big game and used tools made of chipped stone. Between 8000 and 6000 b.c., these early Indians lived principally on the plains and foothills. Around 5000 b.c., a desert climate developed, and game animals and the people who hunted them left.

Buffalo again spread across the region as a more moderate climate developed about a.d. 500. The hunters returned, probably from the south and west, bringing with them new techniques and cultural practices. These early dwellers were probably the ancestors of the Salish Indians. Before the introduction of horses, hunting techniques such as using a buffalo jump, or pishkun, were developed. Entire herds of buffalo would be stampeded off precipices and slaughtered for meat. The use of the tepee, or movable skin tent, was introduced. Pictographs and petroglyphs (rock paintings and carvings) were first made during this period.