Continuity mistake: Indians are on a hilltop and a jet vapour trail can be seen in the sky.
Continuity mistake: In the bicycle riding scene where Butch lets Etta ride on the handlebars, you can see her feet are resting on some sort of pegs protruding from the axle on each side of the bicycle wheel. When she is not riding, the pegs are not there.
Continuity mistake: The Danbys ride in with 13 gunmen. Prudy kills two. Both are shown lying dead in the middle of the street. A few minutes later both dead Danbys are missing from the street and there are once again 13 live Danbys facing Joe stretched over the cannon.
Continuity mistake: Sykes is shot in the right leg, in the thigh area, by the bounty hunters. We see the blood clearly on it when he sits on a rock and holds his leg. Later, when he returns to Aquaverde where he meets Robert Ryan, we see as he sits on his horse that his left leg is bandaged.
Continuity mistake: At the dinner scene when Mattie Ross is trying to obtain Rooster Cogburn's services, Rooster clears the table, and in the next scene he re-clears the table by pushing everything aside to play cards with Chin Lee.
Continuity mistake: At the end of the town collapse, a sincerely drunk Ben dives head-on into a tub where a lady (in her underclothes?) is just enjoying a bath. Propelled by Ben's momentum the tub with both passengers slides down the slippery planks and splashes into the river, while Ben rearranges himself into a comfortable sitting position between shots. If I wasn't completely mistaken also the lady changes her outfit, since the embroidery is missing when they float along. (02:23:35)
Continuity mistake: Inside Moon City, artificial gravity is cited to explain why everything behaves as if under a full Earth gravity. And yet, in scenes out on the untamed lunar surface, everything is still behaving as if under a full Earth gravity.
Continuity mistake: At the end of the movie, when John Wayne followed by the harmonica player is talking to Marian McCargo, her scarf goes from left to right or right to left depending on the angle of the shot. (01:56:00)