The Train Robbers (1973)

After the death of her husband, Mrs. Lowe (Ann-Margret) posts a $50,000 reward in return for help recovering her train-robber beau's hidden fortune, under the pretense of returning it. Lane (John Wayne) assembles a group of cowboys to head to Mexico with Mrs. Lowe, enticed by the reward money. As they cross into Mexico, however, they realize they're being followed, by both a posse of bandits and a single mysterious rider (Ricardo Montalban) with his own agenda.