A device known as a "Running W" was used on the Indians' horses during the sequence where they are chasing the stagecoach. Strong, thin wires are fixed to a metal post, then the other end of the wires are attached to an iron clamp that encircles the legs of a horse, and the post is anchored into the ground. The horse is then ridden at full gallop, and when the wire's maximum length is reached - just when the rider is "shot" - the animal's legs are jerked out from underneath it, causing it to tumble violently and throw the "shot" rider off. The trouble was that the rider knew when the horse was going to fall but the horse didn't, resulting in many horses either being killed outright or having to be destroyed because of broken limbs incurred during the falls. The use of the "Running W" was eventually discontinued after many complaints from both inside and outside the film industry.
When the film was being cast, John Ford lobbied hard for John Wayne but producer Walter Wanger kept saying no. It was only after constant persistence on Ford's part that Wanger finally gave in. Wanger's reservations were based on Wayne's string of B-movies, in which he came across as being a less than competent actor, and the box office failure of Raoul Walsh's The Big Trail (1930) in 1930, Wayne's first serious starring role.
In 1939 there was no paved road through Monument Valley, hence the reason why it hadn't been used as a movie location before (it wasn't paved until the 1950s). Harry Goulding, who ran a trading post there, had heard that John Ford was planning a big-budget Western so he traveled to Hollywood, armed with over 100 photographs, and threatened to camp out on Ford's doorstep until the director saw him. Ford saw him almost immediately and was instantly sold on the location, particularly when he realized that its remoteness would free him from studio interference.
The interior sets all have ceilings, an unusual practice at the time for studio filming. This was to create a claustrophobic effect in complete counterpoint to the wide open expanse of Monument Valley.
John Ford gave John Wayne the script, asking him for any suggestions as to who could play the Ringo Kid. Wayne suggested Lloyd Nolan, not realizing that Ford was baiting him with the part. Once filming began, however, Ford was merciless to Wayne, constantly undermining him. This psychological tactic was designed to make Wayne start feeling some real emotions, and not to be intimidated by acting alongside the likes of such seasoned professionals as Thomas Mitchell.
Near the end of the movie, Luke Plummer (Tom Tyler) has a pair of black aces and a pair of black eights. This is the notorious "dead man's hand" supposed to have been held by Wild Bill Hickok before he was killed.
It's believed by many that the famous line "A man's gotta do what a man's gotta do," widely attributed to a John Wayne Western character, is spoken by Wayne in this film, however, it isn't. His character, The Ringo Kid, instead says "There are some things a man just can't run away from," when asked why he intends to stay and avenge his family's murders rather than try to escape to Mexico.
The hat that John Wayne wears is his own. He would wear it in many westerns during the next two decades before retiring it after Howard Hawks' Rio Bravo (1959), because it was simply "falling apart." After that, the hat was displayed under glass in his home.