When Ben's men ride to town to rescue him there are seven riders on the outskirts, then nine just as they get into town, then seven riding through town, and finally eight when they stop below the room Ben is in.
Inside the hotel room, when Wade fights with Dan trying to
disarm him, Wade falls with his back on the bed and his hat rolls a little way from him. When they take a close up shot of Wade, his hat is almost completely on his head. When Dan orders Wade to get up, they cut to a medium shot and once again, his hat is way over on the bed again.
In the opening sequence the stagecoach is following tracks, presumably made by earlier takes, but during a shot from the driver's viewpoint, the ground is unmarked.
When Wade is handcuffed and set in the stagecoach, his jacket is completely unbuttoned, and remains like this in all shots he appears, until he steps down on Dan's ranch. When he walks toward Dan's house, his jacket is completely buttoned. Once inside the house, the jacket appears in part unbuttoned.
When Charlie comes to the saloon to warn Ben that lawmen are coming, he places his hands on the top of the doors. It then cuts to an exterior view of the doors, and Charlie's hands are not visible.
Tom Butterfield was a real person, but he had died and his stagecoach service had ceased long before the story takes place.
Wade's gang would have killed Dan's wife and children after he left town. Actually, this makes very little sense. They saw their leader jump into the wagon of his own accord, refusing to be saved by them, so they have nothing to take revenge for. What's more, the Wade gang's modus operandi was to kill only when necessary (as explained by Wade himself), and killing Dan's wife and children would go directly against this.
When all the characters are shown in the street just after the clock shows just after 11:00, all of their shadows are extremely long, because the scene was shot probably in very early morning after sunrise.
At about 27:30 when the two townsmen pull back by a wall when shot at by Charlie Prince, you can see the "stone" wall flutter as if it were made out cloth or rubber.
Toward the end when the 3:10 pulls into town, every shot of the sky we see shows no clouds in sight. After Ben Wade and Dan Evans jump on the train it starts to rain rather hard. When the camera cuts back to the train there still is not a cloud anywhere to be seen.
The film is set in the 1880s, but several 1894-model Winchesters are shown.
Most of the clothing worn by the men in the film does not correspond with period dress. This is especially noticeable with Van Heflin fullfront button shirts and Glenn Ford's jean jacket which has stitching that is clearly post-WWII.
As the characters ride into Contention City, modern telephone poles are visible in the background.
The steam locomotive pulling the train to Yuma is clearly of early 1900's vintage. The engine has a steel cab, electric headlight, and other applications that were not available or in common practice in the 1880's.
During the opening credits a long, wispy contrail can be seen across the right two-thirds of the sky.
While the dialog has Bisbee, Contention City, and Benson in about the right place, the footage of Bisbee is clearly Sedona, 250 miles to the north. Coffee Pot Rock stands out there. Contention City shots were filmed at Old Tucson.
Contention City is roughly 40 miles from Bisbee. Unless the party was slowed down immensely, it should have been able to make the trip there in roughly one day.
The early sequences near Bisbee, in the Sonora Desert, ought to have landscape covered with saguaro cacti, but because it was filmed further north in Arizona it does not.
Dan Evans leaves town, despite the fact that Ben Wade had openly threatened that Evans' wife and children will be killed by his gang.
Wade would have noticed that Emmy's eyes were not blue.
Dan Evans leaves his wife and children at the mercy of Wade's gang, who will want to take revenge for his killing of Charlie Prince.
Ben Wade allows himself to get on the train, despite knowing he will be hanged.