The Lost Valley — David Thompson

For even the hardiest of frontiersman, mere survival in the magnificent, uncharted Rockies was a daily struggle against brutal blizzards, wild animals, and bloodthirsty renegades. But to the brave souls who battled the vast frontier, the prize they sought was worth any risk -- complete freedom in an unspoiled world. When mountain man Nathaniel King promised a dying Ute warrior that he would find the man's son, he had no idea that he would soon confront an enemy unlike any he had ever faced. For his trail would lead him and his family straight into the clutches of a mysterious, hidden tribe -- a tribe that no white man had ever seen and lived to describe.