Suzanne Pleshette once said in an interview that her love scenes with Steve McQueen in this movie were horribly awkward for both of them as they had enjoyed a completely platonic friendship since she first came to Hollywood and he had very much taken on the role of big brother to her.
In the scene in the cattle pens when Max (Steve McQueen) fights Jessie Coe (Martin Landau), Max crouches behind a fence and opens the gate to let the cattle out. Some cattle come out the gate while others knock down the fence, and Max must dodge the flailing legs and hooves of the stampeding cattle. The knocking down of the fence was accidental, and McQueen was very nearly trampled for real. Shots of Max rolling clear of the hooves were added when it was decided to use the accidental footage.
Loni Anderson, best known for her role as the buxom blonde secretary "Jennifer Marlowe" on the long-running TV series WKRP in Cincinnati (1978), can be seen in a bit part as a brunette. She's one of the dance hall girls who greets the cowboys upstairs at the hotel while they're cleaning up for a night on the town. She asks one of them, "What's your name? Walter? Hello, Walter."
The name "Nevada Smith" was the original inspiration for the name "Indiana Jones"; the Raiders of the Lost Ark (1981) character's name was originally "Indiana Smith". George Lucas named him "Indiana" after his dog, and "Smith" after this movie. But then it was changed to "Indiana Jones".
The role of Nevada Smith was originally created by Alan Ladd in The Carpetbaggers (1964). A prequel highlighting the Smith character with Ladd was proposed, but the actor's untimely death at age 50 precluded that. Ironically both actors were only 5'7".
The irony of misspelled buckboard sign written McCandles instead of McCanles. The actor John Doucette who plays Uncle Ben McCanles, plays the Sheriff in Big Jake (1971) with John Wayne. John Wayne's character name was Jacob McCandles.