Visible crew/equipment: The scene where Martin and Ethan watch the Cavalry ride in through the river, a car or truck is seen driving up a road to the right and comes to a stop.
Revealing mistake: In the scene out West with the buffalo, notice the car driving in the distant background.
Continuity mistake: When Luz is talking to Jet on the phone for the first time, from the front she's fiddling with the phone cord with her left hand. When it cuts to the reverse, however, her hand is flat on the desk.
Factual error: The movie takes place in the early 20th century (1910s or 1920s or so). When Dean and Jerry are riding in a RR cattle car with its doors open you can clearly see parked automobiles from the 1950s through the open door of the train car.
Factual error: Two grave markers at the end, approximately one hour and 27 minutes into the film, have the date of November 7, 1889, on them. The script made it clear that the climactic gunfight between Glenn Ford and Broderick Crawford came on a Sunday. Ford was called out of church services, for example. According to The World Almanac and Book of Facts, November 7, 1889, was a Thursday, not a Sunday.
Continuity mistake: At the very end of the show when Marshall Cass Silver gets in the carriage with Sally, Sally enters first, sitting on the left and him on the right. When the next shot shows them riding off together in the carriage, they have switched sides.
Continuity mistake: The opening scene states the date as April 10th 1865, the day of the train station robbery. Siringo tells Vance at the school money-raising event that the robbery took place 8 weeks ago, but when Clint is buried at the end, his death is April 25th 1865, only 2 weeks after the robbery.