Visible crew/equipment: At the beginning of the film when being rescued from the quicksand you can see someone's legs and hand behind the horse, holding it. (00:10:00 - 00:11:00)
Revealing mistake: On the way to the border, after Gabrielle has died, when the camera pans it on her face, you can see her eyelids shift and blink.
Factual error: As well as the sergeant's stripes on his cuff, Sergeant O'Neil wears three pips on his epaulettes, which would indicate a much more senior rank and would not be worn together with the stripes.
Continuity mistake: The front view of Sheriff Garrett [Ethan Hawke] while he is talking to Billy shows a stone-walled well between him and the cabin door, but there's no well visible in the rear view. When Billy walks out with his hands up, there appears to be a well to his right (where the horse rail should be visible), but there is no well when Sara and Rio exit the cabin. (00:14:04 - 00:15:10)