Under the Sweetwater Rim by Louis L'Amour Paperback -

Deep in Indian country, Major Mark Devereaux and his men find a grisly scene: a wagon train savagely attacked, with no survivors. One of the wagons originally with the group is missing; in it is a fortune in gold and Devereaux’s daughter, Mary. The slaughter, Devereaux learns, was not the work of Indians but of a murderous outlaw band. With the stakes rising in a deadly game, the only wild card is Lieutenant Tenadore Brian, who is riding with the missing wagon—against orders. Devereaux knows Brian is a good soldier, but is he good enough to protect a saddlebag full of gold . . . and the life of his daughter?