The Tears of God — David Thompson

Nate King knows how tough it is to survive in the rugged wilderness of the untamed frontier. That's why he can never refuse to help someone not as familiar with the infinite dangers of the territory. But when he agrees to guide a freighter captain and his load through geyser country, he has no idea he's stepping straight into the path of a Pawnee with a personal vendetta. No idea that their destination -- the Valley of Skulls -- will live up to its grisly name.