During filming in June 1961, Karl Malden had to be rushed to hospital to have an emergency appendectomy.
Stuntman Bob Morgan was seriously injured, and almost died, while performing a stunt in this picture. Toward the end of the film, there is a gunfight on a moving train between the sheriff and a gang of train robbers. Morgan was one of the stuntmen playing a robber and was crouched next to a pile of logs on a flatcar. The chains holding the logs together snapped, and Morgan was crushed by the falling logs. He was so badly hurt it took him five years to recover to the point where he was able to move by himself and walk unaided.
Cinerama was so expansive that it couldn't really be configured for close-ups. The nearest it could manage was to place a key actor in the central frame and try to get in as close as possible. This proved to be very intimidating for a lot of actors as the camera (an enormous piece of apparatus under a black hood with three lenses) would be literally in their face--18 inches away, to be precise.
Although James Stewart's character was only supposed to be 28 in the movie, Stewart was actually 53 at the time of filming.
Features more than 12,000 extras, including several American Indian tribal members.