Factual error: The movie takes place in 1878. The Indians are all armed with Winchester repeating rifles. Indians of the period were more likely to be armed with old obsolete rifles (Civil War vintage) including some muzzle loaders with prehaps a sprinkling of Winchesters. Also, Indians were very proud of their rifles and usually decorated them with items such as brass tacks; no such decorations are to be seen.
Revealing mistake: At the cave near the end, there are several scenes with the secretary of the interior. These scenes with the main actors appear to be filmed in front of the background as they cast shadows on the other film and the lighting is different. This was most likely done because of budget limitations.
Continuity mistake: When Wyatt Earp is playing cards, a man comes to the table and pounds his fist saying, "You have to listen to this, Marshal." The stacks of money on the table are knocked over by the impact. The camera then looks at only a head shot of Wyatt's disturbed expression at the man bothering him. When the camera looks at the table again, the money is properly stacked again, all within a few seconds.