The Big Sky (1952)

Jim Deakins is a frontiersman and Indian trader who is making a perilous journey with a group of other men up the Missouri River to get a large haul of furs from friendly Blackfoot Indians. The problem is that they have to get through hostile Indian territory first and they find that they have seriously underestimated the difficulties they will undergo. The large body of men who started the journey are gradually whittled down until only a hardy few, like Deakins, are left.