Factual error: Though extremely modest by today's standards, the dress worn by Clara at the hoedown shows far too much cleavage for the time. No schoolteacher would ever wear a dress like that in the 1880s.
Factual error: When Marty goes to meet Mad Dog Tannen for the duel, in the background on the right side is the current flag of California. But that flag did not become the state flag of California until 1911, so would not have been around in 1885.
Continuity mistake: When Marty returns to 1985, he goes to his house and gets in his Toyota pick-up. Look closely behind his head when he first gets in the truck, there is no driver-side head rest. But when he picks up Jennifer, when they pull up to the stop sign the head rest is there. (01:45:00)
Continuity mistake: Watch the scene with the Indians (just as Marty sticks the DeLorean into reverse) and see the differences of how close and far the Indians are from the DeLorean. (00:18:59)
Continuity mistake: When Marty goes back from 1955 to 1885 and meets the Indians, note that none of the Indians shoots any arrows nor do any arrow hit the car. You can see that when he drives the car back into the cave. But when he gets back to the cave after the Cavalry ride, a long arrow sticks out on the side of the car. (00:18:10 - 00:20:00)
Other mistake: When Marty returns to 1985 from 1885 the time machine is destroyed by a train. What is strange is that not only does the train not stop (which is mandatory in the event of an accident) but there is also no reaction from people nearby, such as those in the vehicles waiting to cross the track at the level crossing. Later, when Marty returns to the site with Jennifer, there is still no sign of police officers or other officials.
Visible crew/equipment: In the saloon scene where Doc passes out, a production light with barn doors and stand can be seen in the upper left over Marty's shoulder.
Factual error: In 1885 when Maggie McFly asks Seamus for a word, they walk into the other room and behind them are a few garments hung on pegs on wire hangers. The wire hanger was invented by Albert J. Parkhouse in 1903, eighteen years later. (00:25:50)
Revealing mistake: At the end, when the train destroys the time machine, right at the moment when it hits you can see a small explosion, which was used to trigger the destruction of the time machine. (01:43:03)
Continuity mistake: When the train is coming and is about to run over the DeLorean, the shadow of the train on the wall shows that it is only the locomotive. When the camera changes view, it is a train with freight carriages. (01:43:00)
Continuity mistake: When Doc drinks the 'wake up juice', he runs out and puts his head in the horse trough full of water. However, after a shot to Mad Dog Tannen, his shirt is mysteriously dry again. (01:20:05)
Factual error: At the end of the train scene just before Marty travels to 1985, the train busts through a road block warning that there's only 1/4 mile of track left before the ravine. Keep in mind that the train is travelling at approximately 70-80 mph by this time. At 70 mph (and not even accelerating) it would only take the train 13 seconds to reach the ravine. The actual time in the movie is at least a minute. (01:40:31)
Suggested correction: This can't really be classed as a factual error because we don't know how much of the track has been built since that barrier was put up. They could've put that barrier up when there was only 440 yards or so of track left, but have laid another 800 yards of track since then. I myself actually work on the roads; if we're resurfacing a road, we don't move the sign 100 yards further up the road every time we've resurfaced 100 yards. That sign stays there till we're done, regardless of the distance.
Continuity mistake: When Marty is being chased by the Indians, a wide shot with the DeLorean at the bottom of the screen coming towards us and the Indians following reveals the entire background for a mile or two. However, there are no cavalry visible anywhere despite the fact that they pass over the cave in the following shot only five seconds after the last Indian does. (00:19:15 - 00:20:20)
Revealing mistake: When Marty and Shamus are sharing a meal at the dinner table, Shamus passes Marty the plate of rabbit. As Shamus hand moves away to let go of the plate, to the bottom right hand corner of the plate, a purple patch appears briefly where the two M. J. Fox actors interact, an error with the Vistaglide camera tech used back then. Easier to spot on Blu Ray Version, better than DVD. (00:24:10)
Continuity mistake: When Marty is shot by Buford, he is thrown off his feet and lands on his back. As he does, his poncho flips up, showing his shirt all the up to the middle of his chest. The stove door he is supposedly using as a bulletproof chestplate is conspicuously missing. (01:27:20)
Continuity mistake: In the last fifteen minutes of the film Marty wears his Wild West clothes, including his brown woolen poncho. The front of the poncho is unmarked, completely intact. Shouldn't it have a bullet hole in it? (01:43:50)
Factual error: Standard gauge for railroad tracks in 1885 was 4ft 8 1/2 inches. The distance between the center of the wheels on a Delorean was 5ft 3 inches. The car would not fit on to the tracks, and we can see the wheels aren't recessed or otherwise altered.
Continuity mistake: When Marty is about to go back to 1885, he starts driving and you see him pass the building: then when it shows the car's tires, you can see he passes by the same building again.
Continuity mistake: When Clara first sees the train and starts after it on horseback, it is on her right side. She is at the top of a hill and starts down after the train. In the next shot shown from the front of the train you see the horse appear so the train is on Clara's left. (01:34:09)
Continuity mistake: When the DeLorean is being pulled by horses, the clouds in the sky change in the next shot. (00:38:50)
