Soldier Blue

Soldier Blue is a movie starring Candice Bergen, Peter Strauss, and Donald Pleasence. After a cavalry patrol is ambushed by the Cheyenne, the two survivors, a soldier and a woman, must reach the safety of the nearest fort.
After a cavalry group is massacred by the Cheyenne, only two survivors remain: Honus, a naive private devoted to his duty, and Cresta, a young woman who had lived with the Cheyenne two years and whose sympathies lie more with them than with the US government. Together, they must try to reach the cavalry's main base camp. As they travel onward, Honus is torn between his growing affection for Cresta.