Factual error: The El Paso newspaper is dated Monday June 15 1872. June 15 1872 was a Saturday. (00:48:14)
Revealing mistake: After Manco beats up Cavanaugh and places Cavanaugh's back up against the bar, while Manco faces him, three of Cavanaugh's henchmen appear at the entrance of the bar demanding that Cavanaugh be released. Manco turns around and kills all of them with his pistol, while Cavanaugh falls to the floor crawling toward his gun. Manco is walking toward the entrance of the saloon with his back to Cavanaugh. Manco draws his gun and kills Cavanaugh without looking at him. If you look closely at the tip end of the pistol, you can see that the only thing that Manco would have killed was the saloon floor. (00:17:00)
Deliberate mistake: Near the beginning, Col. Mortimer takes down a wanted poster and goes after the man. The man he kills looks nothing like the man pictured on the poster.
Suggested correction: There is a similar situation in the UK produced western movie "Carry On Cowboy" (released 1965). Johnny Finger/The Rumpo Kid (Sid James) shoots the sheriff of a US town. The sheriff is related to legendary sharpshooter Annie Oakley (Angela Douglas) and she swears revenge. Finding that Johnny Finger is staying in a saloon, Annie Oakley sets up a trap on the staircase. Another person (an uncredited extra) inadvertently walks up the staircase, so she shoots him instead. As he falls down the stairs she calls out "I'm terribly sorry I thought you were somebody else." Perhaps Col Mortimer has made a similar mistake. Being less polite than Annie Oakley he does not have the good manners to apologise.
Suggested correction: Is that a mistake? (Either on the part of the people who made the film, or assuming this was real life, on the part of Colonel Mortimer?) They're a pretty bloodthirsty lot in this film, and nobody seems to really care who gets shot. Maybe he figures he can get a bounty for that person anyway.
Continuity mistake: Near the beginning when Lee Van Cleef looks at the the wanted poster on the ticket booth at Tucumcari (just after getting off the train), there are two extra zero's drawn onto the poster (as added by the villain). Van Cleef then takes this poster away with him, and slots it under the door of a hotel room on a later scene - notice that the additional zero's have since disappeared from the same poster. (00:06:30 - 00:09:20)
Continuity mistake: When Monco drives away with the dead bandits a tail gate of the cart is swinging freely. A few seconds later - after having retrieved the money bag from the tree and driving away 'into the sunset' - the tail gate is not there. (02:04:35)
Revealing mistake: During the "dream sequence", Indio shoots the young man several times, yet there's neither blood nor bullet holes on his shirt, front or back.
Other mistake: At the beginning of the film, you see Colonel Mortimer traveling on a train while reading a bible. He has a Indian squaw and a gentleman wearing glasses and a derby sitting across from him. A conductor comes by to pick up their tickets. Colonel Mortimer asks the conductor, "is it far to Tucamcari?" The conductor replies, "we pass there in three to four minutes." The gentleman with glasses starts to tell the Colonel that he is on the wrong train. As he tells him this, look out the train window and see a car driving off into the distance. (00:04:30)
Audio problem: When Lee and Clint are shooting each other's hats the sound of a ricochet can be heard on almost every shot, even when shooting at a hat in the air.
Revealing mistake: While Lee Van Cleef is browsing the news-journal, we first see a front page, followed by 6 identical consequent pairs of pages and then again the same front page from before. Also, the text doesn't seem to be text at all. (00:48:10)
Continuity mistake: Monco's and Col. Mortimer's hats are remarkably undamaged after having received six and four bullets respectively. Stetsons are not soft enough to just fly away with the bullet. There should be some holes in them. (00:54:55)
Continuity mistake: The wagon that Marco initially loads all the bodies onto - and the position of the bodies - then changes completely in the next shot as Marco retrieves the saddlebags and rides off into the distance.
Factual error: There's a plane in the sky above Clint's hat in the shooting hats scene.
Continuity mistake: When Col. Mortimer slots the poster under the door, the paper changes side between shots.
Continuity mistake: The "Man With No Name" rides out of town after collecting his reward for Cavanaugh on a red colored horse. He arrives in El Paso on a brown horse with a different saddle. After he kills the three men he was sent out with to rob a bank he mounts a brown horse but arrives at the telegraph office on a red horse. It is obvious he rode straight to the telegraph office. He leaves the telegraph office and is riding the brown horse again.
Continuity mistake: When Manco goes to the saloon in search of Cavanaugh, he is outside in pouring rain. Yet he enters the saloon with neither his hat nor his sarape wet.
Revealing mistake: About an hour and a half into the movie Clint Eastwood forces a telegraph guy to send a fake message saying the bank is being robbed, in a nearby town - as a ruse. In the next scene, when the posse rides down a dirt road, you can see tire tracks as they are all coming down a hill and going around a bend.
Continuity mistake: After Monco brings Sancho Perez back to Indio's hideout, one of Indio's henchmen shoots the tip end of Monco's cigar off. When Monco relights that cigar, the cigar is longer. Immediately after, Indio lights his cigarette with that cigar, and it gets shorter. (01:06:00 - 01:07:00)
Other mistake: The man with no name goes through roof to get the money. The director put him in blackface to darken his skin so to only focus on his eyes and mouth. Not a very good job. You will see leading up to the roof and when he jumps down from the rafter to encounter the Col. Douglas Mortimer, his face is clear of makeup. I guess it was the best they could do to get the lighting they wanted during the scene.
Continuity mistake: When Manco plays poker with Cavanaugh, he has three aces in his hand and Cavanaugh has three kings. When Cavanaugh puts his hand down, his three kings are from bottom to top. When Manco lays his hand down, Cavanaugh's three kings are now from top to bottom.
Factual error: Two errors. The money in the safe is Confederate. It was worthless in 1872. Tucumcari didn't exist in 1872. The place which later became Tucumcari only came into existence in 1901 and wasn't named as such until 1908.