Capt. Roper is in a gunfight in Death Valley and is shot in the left shoulder. When riding into town his right arm is in a sling.
When Capt. Roper is camping with his troop for the night and hears the noise of Mescaleros chasing a stagecoach the scene goes from night time to bright sunny day to night time again by the time the stagecoach comes to a complete stop (19:07 to 20:18).
Near the end William Holden gets shot in the left arm when challenging the Indians but at the very end of the movie his right arm is bandaged instead.
Director John Sturgess likes to dress his P.O.W officers in their dress uniforms. Common sense would dictate that a soldier is usually not wearing his dress uniform when captured and wouldn't get issued one while in prison.
There were no Union Civil War POW camps in Arizona. In fact the closest one to Arizona would be a Confederate one in Tyler, Texas.
All the Union soldiers were wearing brand new uniforms and boots.
Carla has so many outfits that is stretches credulity.
The ladies' dresses had zippers, which were not invented until 1913.
"Oh Dem Golden Slippers", which is heard in the saloon in Lordsville, was written in 1879;
The music at the wedding reception is "My Darling Clementine," which wasn't written until 1884.
Almost all of the US soldiers including the Confederates are wearing the very same US Army pattern 1883 drab campaign hat.
Lt. Beecher scans the horizon with a very modern pair of binoculars.
Although the film is set in Arizona, when Captain Roper is with Carla Forester in the camp after he rescues her from the stagecoach, towards the beginning of the movie, the matte painting clearly shows Devil's Tower which is located in Wyoming.