Filming on this movie coincided with that year's Academy Awards. Co-star Martin Balsam was a Best Supporting Actor nominee for Des clowns par milliers (1965), but did not receive permission to leave the set. Balsam sneaked off to attend the ceremony; he won the Oscar.
Steve McQueen was offered the role of John Russell but turned it down because it reminded him of Nevada Smith (1966), in which he played a half-Indian. After the release of this film, McQueen said it was one of Paul Newman's best roles.
Film vs. Novel: Jessie Brown, portrayed Diane Cilento, who comprises a large amount of screen time and dialogue, doesn't exist in the novel. Nor does Margaret Blye's character Doris Blake, the wife of Billy Lee Blake, the young stage line worker portrayed by Peter Lazer, whose character in the novel is a bachelor. The only other female character who rides in the mud wagon in the novel besides Mrs. Favor (played by Barbara Rush) is a seventeen year old woman recently released from Apache captivity.
Intense rainstorms made the shooting very difficult. Paul Newman, during that time, played tennis, got drunk, and engaged in bawdy conversations with Martin Balsam.