Archaeologists believe that the first Americans migrated across the Bering land bridge from Asia between 12,000 and 30,000 years ago. They followed the Great North Trail, which dipped down into Montana along the east slope of the Rocky Mountains. These Paleo-Indians or Clovis people hunted the now-extinct mammoths and bison with Clovis points. Clovis points dated 12,000 to 13,000 years old have been found along the Missouri River near Townsend, Montana, about forty-five miles beyond the Jefferson. Paleo-Indians seldom entered the Rockies, where glaciation persisted.