John Wayne was so impressed by Christopher George's performance as the villain with a moral code that he told him during filming that he was going to work with him again. He kept his word and rehired him for Chisum, Uma Lenda Americana (1970) and Chacais do Oeste (1973).
The opening credits feature a montage of original paintings that depict various scenes of cowboy life in the Old West. The artist was Olaf Wieghorst, who appears in the film as gunsmith Swede Larsen.
The bathtub scene was largely Robert Mitchum's invention. Members of the crew were laughing while it was being filmed at the idea of Mitchum being embarrassed in front of a woman.