Continuity mistake: When Mongo enters Rock Ridge on the steer, the cuff on the chain around his neck instantly switches from open end facing left to facing right in the next cut.
Continuity mistake: Near the end after the mob goes over the cliff and Jim is chasing the horses through a snow patch, another rider on a light colored horse can be seen on the right. (01:36:00)
Character mistake: The 4 brothers have just rode into town and are securing their horses. On the flag pole in the background the Texas flag is upside down. Note: The correct way is white flies on top and red on bottom.
Visible crew/equipment: When the young lady is trying to drag her dead husband away to bury him, as she takes a hold of the blanket you can see the covered wagon in the background and someone's legs behind the wheel begin to move to the right. She was suppose to be alone except for her dead husband. (00:34:00)
Other mistake: When in the tub in Arkansas, Wyatt is bare chested. In bed with Josie he's suddenly sprouted a lush garden of chest hair.
Factual error: In the train scene near the start there are vapor trails from modern day jet aircraft in the sky above. (00:06:15)
Revealing mistake: After Jim's horse is shot from under him while running down the really steep hill, and Jim later regains consciousness, before he turns and finds his horse dead, if you watch closely you can see the horse still breathing.
Factual error: Towards the end when the cavalry uncovers the American flag, it has 50 stars.
Factual error: So the Civil War ends, and the colonel heads for Texas. It must have taken close to a decade to arrive there, for when he rides into Blackthorne, Texas, he's packing a Model 1873 Colt, and a Model 1873 Winchester.
Continuity mistake: In the final fight scene between John Wayne and the bad guy, Wayne gets struck in the head, and as he falls backwards over the wagon tongue his toupee lifts off.
Continuity mistake: McQueen and Brynner take a hearse up the hill to deliver a coffin to the graveyard. When they go back down the hill, you can see a plume fall off one of the horses' heads, but in the next shot, the plume is back on. (00:16:05)
Visible crew/equipment: When Jim West is hanging by the rains of the horse you can see the rider's boot as Jim West is telling the horses to back up.
Factual error: Near the end of the film Butch is complaining about the living conditions they have to endure - jungles, swamps, snakes, night work - and Sundance sarcastically retorts "Bitch, bitch, bitch!" In 1908 the term meant just what it literally means: "Female dog." It did not adopt its current meaning of "complain" until much later. At the time the film is set - outside the context of "female dog" - it was considered to be a serious obscenity, and it would not have been used to describe something as ordinary as someone moaning about his living conditions.
Factual error: John Wayne and James Caan are in the gunsmiths shop, and behind the gunsmith on the shelf are some products, one of these products is Bugler tobacco. Bugler tobacco was introduced in the United States in 1932. (01:00:00 - 01:02:00)
Other mistake: In the very last scene of the movie, and just before Blondie shoots the rope that is holding Tuco on the grave's cross. You can see a car moving in the background, screen right of Tuco's head.
Visible crew/equipment: When they get into a horse drawn carriage, there are glass windows. When the carriage turns the corner you see a reflection of a white Dodge pickup truck.
Revealing mistake: In one of Pickett's charge scene the bayonets are obviously rubber.
Other mistake: There is a patch on the jacket Harley (Rourke) wears, that appears and disappears throughout the movie. It's on the front lower right side. It is there when he's standing outside their friends' bar with Marlboro, it's gone when they are inside.
Continuity mistake: In the scene when Billy is shooting Doc's handcuffs, Billy's revolver changes several times, shot by shot. Watch for the front sight to appear and disappear between the POV Doc shot and the medium distance shot, and for the entire finish of the gun to change at least twice.
Continuity mistake: Near the end of the film when Spider Mike is rescued from a town. The Rubber Duck's truck is damaged. It loses the bullbars on the front, and the windbreaker on the roof is flattened against the roof of the cab. Yet after leaving the town, in a series of shots showing the Rubber Duck's truck. The damage disappears or varies. The windbreaker appears fixed and so do the bars, but in the next shot just the windbreaker is fixed and the bars aren't. It continues like this through a montage and then in the next scene when it cuts back to a close up of the truck both are damaged again. (01:47:40)