After drawing his gun, Tom Mix's gun is in his holster and in his hand at the same time throughout the gunfight at his ranch.
In the opening scene, the cushions on the stage disappear and reappear between shots.
One of the movie star doubles at the Candy Store is dressed like Mae West. The film takes place in 1929. West's big screen debut was in Night After Night (1932).
The inaugural Academy Awards is depicted as an evening dinner function. In real life, it was a brunch presentation.
When Tom Mix chases down the Stagecoach after the driver is shot, the reins go through a "window" into the stagecoach so a stunt driver can control the team.
In the restaurant, one of the musicians in the mariachi band plays an Ovation guitar, first introduced in 1964.
During the stagecoach chase in the beginning, modern power lines are visible in the background.
When Wyatt and Tom land the plane in the grassy field, the tires screech as if they were landing on a paved runway.
The final shot shows an eastbound train leaving Pasadena and chugging into the sunset, which means the sun is setting in the East.
Wyatt Earp says that Calamity Jane's real name was Mary Jane Cannary. Her first name was actually Martha.
Tom Mix was right handed, but Bruce Willis (who is left handed) plays him as a lefty. Note especially the left handed gun holster.