Anachronisms: The film says that news of the Battle of Little Big Horn (1876) was spread by the Pony Express - which went out of business in 1861.
Anachronisms: The calendar page that Capt. Brittles uses to mark off the days until his retirement is for the wrong month. The calendar most unusually shows the year but not the month, but it does show that the month has 31 days and begins on a Wednesday. Therefore, the only month in 1876 that this page would have fit was March. But it cannot be March, because it refers to the Battle of the Little Big Horn as having recently occurred and that Battle did not take place until June 1876. Arguably, the calendar should show the month of July, because John Wayne's character indicates that it is the 5th of the month, and news of Custer's death at Little Big Horn on Sunday June 25 would have taken about two weeks to arrive by (anachronistic) pony express.
Anachronisms: At the very end of the film the cavalry marches by with a 48-star flag. In 1876 there were only 38 states.
Continuity: When Sgt. Tyree stops the paymaster's stage coach, he walks back past the horses to the coach. In the footwell of the driver's seat there are two holes through which the reins pass. The head of the stuntman who was driving the "driverless" coach is visible.
Continuity: Prior to leaving Fort Stock on his last patrol, Captain Brittles writes an objection to having to take a wagon on the mission. He hands the written complaint to Major Allshard, who in turn hands it to Sgt. Hochbauer, who then reads the report up side down.
Continuity: During the fight in the canteen, when Sgt. Quincannon throws the small soldier over the counter, the barman Connolly has his pipe in his mouth. In the next shot, his pipe is in his right hand.