Revealing mistake: At the end when Needles tries to race Marty, Marty goes backwards and does a reverse 180. When they show the whole truck right when it's turning, you can see the tracks from the previous takes and the dust that helped the truck spin. (01:47:30)
Continuity mistake: When the movie is about to end, Marty picks up Doc's photo. From the front shot he is grabbing it by the middle, but in the opposite angle he holds it by the lower end. (01:48:40)
Continuity mistake: At the very end Doc comes back to 1985 in the train. When the train is slowing down they cut to Marty and Jennifer on the ground and the shadow of the train is not moving. But when they go back to the train it is still slowing down. (01:48:55)
Revealing mistake: At the very end of this film, Doc appears in his locomotive time machine. In every shot the plate which says 'ELB' changes color. From red to orange. You would say this is a change in light angle, but when the locomotive rises and turns, you can see every angle of this plate and in every angle this plate is red. (01:48:55)
Continuity mistake: When the movie ends, Marty and Jen are blown away. They're either landing on shadowy or sunny grass, depending on the angle. This changes back and forth. (01:49:05)
Continuity mistake: Doc comes back from the past. Jennifer walks to stands next to him. In the following shot, she is still approaching Doc to give him the paper from 2015. (01:50:05)
Other mistake: When the movie ends and Doc says, "It means your future hasn't been written yet," watch his son Verne behind. He looks towards the camera and seems unhappy, makes a beckoning gesture (presumably at the crew), and points at his crotch. Seemingly, the kid was having a hard time trying not to pee on himself. (01:50:39)
Continuity mistake: At the end of the movie, when Doc and his family leave in their newly built train, the neon lights that flash over the front of the train go from left to right. In the next shot, where the train actually rises from the ground, they go in the opposite direction. (01:51:05)
Factual error: Though extremely modest on today's standards, the dress worn by Clara to 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.
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.
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.
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.
Plot hole: Although Marty rips the fuel line, not all the fuel would have drained out of the tank. Only the fuel that was already in the fuel line would have leaked out, meaning it could simply be patched, bled and the engine would run without a problem.
Suggested correction: A cut fuel line could absolutely drain the tank. Even if not a direct route with respect to gravity, it could still create a siphon effect and drain the tank.
Factual error: In 1885, Hill Valley and its surrounding areas are shown as having a desert climate, when in both 1955 and 1985, the climate is grassland. In reality, Nevada County, California (where Hill Valley is supposed to be located) is and always has been grassland and forests, not arid desert.
Suggested correction: Hill Valley is in Hill County, as stated at the activation of the clock in 1885.
Visible crew/equipment: When Doc's about to send Marty back to 1885 from 1955 at the open air cinema, you can see the shadow of the camera sticking out from the shadow of the building - it moves as the camera tracks Doc over to the car.
Revealing mistake: When Marty is in the cave with the bear, there are two non-consecutive shots from behind the bear. You can see scruffy, fake-looking fur on the bear in those two shots - obviously someone in a black fur costume. The rest of the shots use a real bear.
Factual error: In the scene where Doc and Clara are playing with a telescope at night, the moon is seen twice. The phase of the moon appears to be a waning gibbous. Though the phase of the moon on the night of September 5th, 1885 at pacific time was waning, it was actually a waning crescent, a much different looking phase of the moon. I looked this up on the United States Naval Observatory website.
Factual error: The steam locomotive in the film is of a 4-6-0 wheel arrangement and is lettered as Central Pacific no. 131. The Central Pacific did have 4-6-0 engines in 1885, but according to the company's locomotive roster, the number 131 belonged to an engine of a 4-4-0 wheel arrangement. Also when the locomotive is uncoupled it shows a Janney (fist style coupler) - that style wasn't invented until 1890. The locomotive would have used a pin and link style connection.
