John Wayne was sixty-five years old at the time the movie was filmed. He had had a cancerous lung removed in 1964, and was suffering from emphysema in his remaining lung. Wayne was so weakened that he had to use a stepladder to climb onto his horse in the film. In addition to his own declining health, news that his friend and mentor, John Ford, was dying of cancer forced the actor to consider his own mortality. After Ford's death in August, 1973, Wayne told reporters, "I'm pretty much living on borrowed time."

According to Michael Munn's 2003 biography "John Wayne: The Man Behind the Myth", Neville Brand was surprised to be offered the role of half-Comanche scout Lightfoot, a part, for which he felt he was badly suited, but accepted anyway because he hadn't been offered a better part elsewhere. However it has been questioned whether Munn really met John Wayne or any of the celebrities he claimed to have interviewed.

The opening scene was filmed entirely on a fragmentary set, augmented by matte paintings, on a Warner Bros. sound stage.

John Wayne later said, "It just wasn't a well done picture. It needed better writing; it needed a little better care in making."

Most of the scenes showing John Wayne riding from a distance were filmed with stuntman Chuck Roberson substituting for Wayne. Roberson also appears briefly as the leader of the posse.

Continuity

As the two boys ride away from the boarding house, the lady goes up to the steps in the shade. The next shot shows the boys farther away from the house which has the steps in full sunshine.



Factual errors

While not technically an error, the use of four separate levers and traps for the gallows was for dramatic effect and would not have been done if this was real. As seen in the quadruple executions of the Lincoln conspirators in 1865, the easiest way was to use one lever and one wide trap.



Revealing mistakes

After Cahill catches onto his sons' involvement in the bank robbery, he and Lightfoot watch the boys as they're fishing. After the boys have traveled a while in the buckboard, the two men are seen watching the boys again from afar. The medium shot of Wayne and Brand shows that they're sitting on their horses in the very place from which they had been watching the boys fishing.

Rain falling at two different and constant angles when Billy Joe Cahill hides from Abe Fraser in the farmyard.

Many of the long shots of Cahill are obviously not John Wayne. From Trivia: Most of the scenes showing John Wayne riding from a distance were filmed with Chuck Roberson substituting for Wayne.

Lightfoot's horse has a saddle under the blanket. You can see stirrups hanging under the blanket and in a latter scene, Cahill uses them to mount Lightfoot's horse. Half-Comanche scouts are allowed to put blankets over their saddles.



Plot holes

When Cahill first began to seriously suspect his sons were involved in the robbery he should have tried to force them to tell the truth about it.

There is no explanation for why the two Cahill brothers have completely different accents.

Billy Joe says he is nearly 13, yet Danny obviously already knows his brother is only 11.