Factual error: Towards the end when the cavalry uncovers the American flag, it has 50 stars.
Continuity mistake: When Rick Nelson tells Angie Dickinson to throw the plant pot through the window to distract the gunmen who threaten John Wayne he seems to have had a hair cut between scenes as his sideburns are halved by the time he reaches the street and grow again later.
Visible crew/equipment: Michael Pate is walking down the street in this western and as he passes a shop window you can see all the camera crew, the director, the arc lights etc.
Continuity mistake: Whit and Boone are watching the freshly widowed Mrs. Lane and entertain some fine vintage sexist talk about her need for a new man. At the end of it, Boone slaps his buddy with a wet hankie on the cheek and it limps on the shoulder. James Coburn laughs and squeezes his buddy's gift tight in hand, but in the next shot it is back on his shoulder. (00:41:35)
Continuity mistake: When Bugs is performing his shooting stunt in the saloon, you can see the entrance behind Sam has nothing between it. When Sam tells Bugs he's missed, we cut to Bugs who says "Wait!" and then return to Sam, and this time there are doors between the entrance.