First, I'd like to go back in time about 15,000 years ago. The first humans migrated to this continent about 15,000 years ago; they may have come a little bit earlier but we know they came across the Bering Land Bridge during periods of glaciation when this was dry land. At this time, there were a lot of Pleistocene mammals that were beginning to go extinct such as Mastodons, Saber Tooth Tigers, horses, and camels. Also, at this time, the first Grizzly Bears migrated from Asia to North America about 15,000 years ago. They came along the same route and probably interacted with humans along the way.