The locomotive, Central Pacific no. 131, in the film featured a Ten-Wheeler arrangement of 4-6-0. While the Central Pacific did have such locomotives in 1885, the number 131 actually belonged to an American type, which had a 4-4-0 wheel arrangement.
After Marty arrives in 1885, he eats dinner at his great-great-grandparents' house. During dinner, Maggie asks to talk to her husband privately in the other room. In that other room, wire hangers are hung on the wall behind them. Wire hangers were invented by Alfred J. Parkhouse in 1903.
In one shot during the aftermath of Marty's "shootout" with Tannen, a modern California state flag can be seen hanging from one of the buildings. This design was not developed until 1911, the original having been destroyed in the Great San Francisco Earthquake of 1906.
The bulk of the film takes place in 1885. All of the windmills seen in the film are Aermotor self-oiling models. The Aermotor company wasn't formed until 1888, and the self-oiling model wasn't developed until 1915.
When Doc Brown demonstrates the plan on the model of the railroad, the words POINT OF NO RETURN are written on a book. That book is The Young and Field Literary Reader: Book 4, which was originally published in 1910.
When Doc and Marty commandeer the locomotive they tell the train crew to uncouple the cars from the tender. The couplers, however, are modern AAR-type knuckle couplers, the earliest versions of which weren't adopted by US railroads until after an act of Congress in 1893. Most couplers prior to then, and even for some time during the transition period, were the older, more-dangerous link-and-pin design.
During the Hill Valley Festival in 1885 where the courthouse clock is dedicated, a sousaphone is seen in the background playing with the band. The sousaphone was not created until 1893 by the J.W. Pepper company.
Before Marty heads to 1885, Doc sets the time circuits to an 8am arrival time. Shortly after arrival, Marty is rendered unconscious, and according to Maggie McFly, awakes nearly 6 hours later. This would make it around 2pm. It would not be dark outside, nor suppertime.
In 1885 the train engineer is wearing a traditional striped hat. This type of hat was invented by George Kromer in 1906. In 1885, railroad men wore the same type of hats as any other person engaged in physical labor.
While the band is playing at the town dance, the banjo player is playing the 3 finger banjo style. This style of playing wasn't invented until the 1920's, 35 years later. And wasn't made famous until 1946 by Earl Scruggs.
Towards the end of the film, Mad Dog Tannen is holding Doc Brown hostage trying to lure Marty out into the street for a duel. He tells Marty that if he doesn't face him now, he will shoot Doc Brown. When Marty doesn't come out, Tannen pulls his single action Colt pistol and points it at Doc's head. When he does this we can hear the distinctive clicking sound of the hammer being cocked as he's raising the gun, but his thumb never actually touches the hammer at any point when he draws his pistol.
On each of the occasions when the Delorean door is closed, it fails to make the electronic sound as it does when it's opened. The door should also make the sound when closed as evidenced in parts 1 and 2.
The 1955 Doc states that his future self might have landed in the Dark Ages and been burned as a heretic. However, it's shown throughout the trilogy that the DeLorean can only travel through time and not space, so the 1985 Doc would have landed in California in the Dark Ages (circa 1000-1500 A.D.), at which time Christianity was unknown to the locals.
When Doc Brown and Clara are talking about Jules Verne's 20,000 Leagues under the Sea, Clara states that the book was written 10 years before. In fact, 20,000 Leagues under the Sea was published in 1870, 15 years before 1885, when the movie takes place.
Doc tries having a team of horses pull the time machine, but during the 'experiment,' he says it's no use -- not because of what he observes in the 'experiment' but because of what he already knew about the physical limitations of horses. He conducted the 'experiment' for no reason (except visual humor).
Lea Thompson plays both Lorraine McFly (Marty's mother) and Maggie McFly (Marty's great-great grandmother). Barring incest, it would be nearly impossible for the two characters to resemble each other so closely, since Lorraine could not be descended from Maggie.
When Marty sees the unfinished ravine train tracks in 1885, he tells Doc that they can scratch that idea. Doc explains to Marty that the rest of the tracks across the ravine will exist in 1985, at which point they will be able to safely cross the ravine. However, Doc knows the ravine will be an active railroad track, but never seems to consider the possibility they could arrive back in 1985 and strike an oncoming train. This is almost exactly what happens when Marty arrives back to 1985.
After the scene in the saloon with Mad Dog and Marty, Mad Dog has a soiled shirt due to the spittoon. In the following scene when Mad Dog and his cronies are chasing Marty on their horses, Mad Dog has a clean shirt.
When Doc says "I put gas in the tank", the shadow of the building stretches only to a few feet past the DeLorean. But two lines later, when Marty says "Hoverboard" and gets it, the shadow has stretched all the way to Doc's 1955 car.
When Clara is on the train to leave town, she pulls a cord to trigger an emergency stop. Her hands are clad in dark brown leather gloves. However, right after she gets off the train and begins running, her hands are not gloved. She is then seen wearing these same gloves throughout the remainder of the film.
When Buford Tannen starts to hang Marty at the new courthouse, we see 'Mad Dog' whip one loop of rope around Marty's neck before he pulls the rope tight to tie it to the hook. After Marty is pulled up into the air we see a closeup of him with his fingers inserted into at least three loops of rope around his neck.
The shadows during the showdown: the camera angle from low down behind Marty shows him in full sunlight from the front, in other shots the sun is clearly throwing shadows at angles to Marty. After he's being shot, Marty ends up well into the shadows of houses.
The telescope changes position in Emmett's hands while he's talking to Clara in the barn. This is evident from the position of the adjusting wheels on the side of the telescope. Their position keeps changing showing the telescope is being rotated, but throughout the conversation, Emmett never moves his hands in that manner.
During the scene where Doc places the old white wall tires from 1955 on the front of the train as padding against the bumper of the DeLorean, he places the front tire with the white wall facing outward towards the bumper. Later as the train careens off of the uncompleted bridge, the tires are visible and none are white wall tires.
Doc rides bareback to tell Clara goodbye (his unsaddled horse is hitched at the saloon the next morning). Likewise, Marty rides bareback to find Doc that morning. Yet both jump on saddled horses after the gunfight to catch the train.
At the beginning, while Doc is dictating into his tape recorder, Copernicus is on the right side of the couch. As Marty says, "Hey Doc," Doc turns around and screams. As he screams the camera cuts to a view of Marty, and Copernicus is on the left side of the couch. The next instant as Doc is falling backwards, Copernicus is seen on the right side of the couch again.
When Marty is transported to 1885, he runs into the real Indians...while he is turning around and starts driving away, the Indians are about 50 FEET away from him. They changed shots of that scene three times as Marty is driving away, each time the Indians were moved back to about 50 YARDS as the perspective changed...
When Tannen is shooting at Marty in the saloon and making him dance, the position of the spittoon changes. Also the board he kicks only appears loose and out of shape just as he's about to stomp on it - prior to that it was a solid, smooth wooden floor.
When Marty is facing Mad Dog in the street, Tannen tells Marty to draw and Marty says "NO". There is a close up shot of Sheamus and Chester the bartender standing near each other with a post in between them, and 4 or 5 cowboys standing immediately behind them. When the camera cuts to shot of Doc Brown and Tannen's henchmen, you can see Sheamus and Chester behind them on the porch of the saloon, but now they are standing nowhere near the post and about 10 feet apart and there are no longer any cowboys behind them. This happens a few times during this scene.
Clara's belongings go over the edge of the ravine. Later, she asks the doc to align her telescope. A brass telescope being dropped as her belongings were would be smashed, yet her's is not even dented.
When Marty is running away from Buford Tannen and his gang after their first encounter at the saloon, a crewmember in blue shorts and a white t-shirt is running alongside a camera on the left side of the screen.
Towards the end When Marty questions the people in the bar by saying," What...what if I don't go out there?" On Marty's right, a film light on a stand is clearly visible sitting in front of the window.
When Marty first arrives in 1885, he's driving (and running) around red brush-covered desert terrain with monolithic geography on the horizon. As he runs over a hill away from a bear, he stumbles down a hillside and crashed into Seamus McFly's fence. As the camera pans up to Seamus, the countryside is lush and green, with rolling hills. Indicating that the desert scenes in the movie were all filmed in Monument Valley which is in Arizona, and not California (which Hill Valley is in).
When Marty is in the cave with the bear the scene looking out of the cave shows the desert going on for miles. But when he runs out of the cave there is a little hill about 300 feet out, with the cliff just beyond it.
Trains going to Hill Valley in 1885 are marked "Central Pacific." Clara asks the ticket agent where is the end of the line? The agent says "San Francisco." The CPRR did not go to San Francisco. It ended in Oakland and a ferry connection was required to reach San Francisco.
When Marty arrives at the Hill Valley railway station, the camera lifts up over the station to show the town, and the Town Hall can be seen under construction up the hill. However in all the future scenes the town square in front of the Town Hall, and all the immediately surrounding land, is flat - there is no hill.
When the three logs "blow" the locomotive suddenly accelerates. All the logs do is burn hotter than normal but there would still be an appreciable time-lag since the water in the boiler has to be heated. Therefore the acceleration would be slower and there would be no burst of speed.
When Doc Brown and Marty have transported the DeLorean to the drive-in theater and are preparing to launch it toward the screen and into 1885, Marty shows Doc Brown that he is ready by enthusiastically slamming the transmission's gear lever to the left and down. The director got the shot he wanted, not realizing that for the car's shift pattern, moving the lever that way would put the DeLorean into reverse.
Doc wakes up on a Sunday morning in November 1955 at 7:00 a.m. to a television broadcast of Howdy Doody. In 1955 that program came on weekday afternoons, even in the Pacific time zone. It never aired on Sunday.
When the train is stopped short of the switch track, Marty jumps off and changes the switch and the crew disconnects the train behind the tender. Doc Brown then starts the train and moves on to the switch. When the camera angle changes to see from the front looking back the detached cars are too close to the switch to allow for the space of the engine and tender.
Just as Marty gets into Hill Valley in 1885, there's a building that says "Wells Fargo" on it. The Bank company we know today did start in California (when it was still a territory) during it's famous 1848 Gold Rush, but it was a financial consultant by the time of 1885 and was not a bank until well into the 20th century.
The Time Machine has a Fusion Reactor to power up the time circuits and the Flux Compactior. So, if it got hit by a train, it wouldn't just have a little explosion which caused the destruction of the Time Machine. It would've leveled about half of Hill Valley, killing Marty and destroying the train that hit the Time Machine.
The 1955 Doc has stated that he supplied the Time Machine with gasoline. In 1955, it was still the norm for gasoline to have lead in it. Any car that was made after 1975 are designed to not run on leaded gasoline, so putting leaded gasoline to a 1985 modeled car (like the DeLorean) would be dangerous to the car. Though, with Doc's brilliant scientific mind, he would have found a way to extract the lead from the gasoline, which is unlikely.
George McFly's great-grandmother looks just like his wife. It may just be coincidence that Maggie and Lorraine look alike, implying that McFly men have always been attracted to women who look like her. Or this could be an allusion to the notion that in small communities people often choose their own distant (or close) cousins as mates.
For Marty to avoid crashing into a tree that once existed in the past, Doc felt it was safe to send Marty back to 1885 at a drive-in as he says, "this was all wide open space". Some viewers have questioned how Doc could know this information. However, it is entirely possible that he looked it up at the library before leaving (also, he could have gone back before or while repairing the DeLorean, which would take at least a couple of days anyway, even assuming he already had everything he needed, which is unlikely) or that he, or a friend of his, had a map of the general Hill Valley area as it was in late 1885 in his possession.
When Marty and Doc look at the Delorean's damage. Doc notes that the car needs parts and says, Where are we going to find gas/parts for the Delorean at this time?
If they went back to the cave where Doc put the Delorean for Marty to find, he could have gotten the parts from there. But if they took parts from the hidden Delorean, they would create a paradox because if they damaged the past Delorean then the Delorean that Marty used would be damaged to the point where the "1955" Doc Brown could not fix it, which would mean that Marty could not go to 1885 to rescue the "1985" Doc Brown and damage the Delorean that is in the cave.
The complex logic, and conflicting theories, of time travel have resulted in a great many potential plot holes, especially when the movie is viewed in the context of the whole trilogy. But time travel movies are like that.
Marty wears his red and white colored Nike sneakers throughout the film; but when Marty and Doc Brown are in the mine in 1955 to find the DeLorean, he is wearing black and white Converse Taylor's or "Chucks", that is because underneath the brown jacket, Marty is wearing his 1955 outfit he wore in the first film.
At the end of Back to the Future Part II, Marty sets the hover board on the ground while burning the book and doesn't pick it up at any point and doesn't have it in his possession when he gets the 1955 Doc to help him get to 1885, but it is still seen in the car when he goes back to 1885, even though it was apparently left at the sign. Marty does in fact have it in Doc's house at the beginning of the movie, and it's implied that a few hours have passed between films, so Marty would have had time to run to the sign, get the hoverboard back, and bring it to Doc's house.
In Back to the Future Part II, Doc gets sent back to 1885 after lightning hits the DeLorean. But in Back to the future III, Marty goes back to "save" doc. When this happens, there are two DeLoreans in 1885. This is not an error and is what happened. It is possible, Doc did not want to use the first car as not to mess up the time line so Marty could return to save him.
The 1955 Doc has installed batteries for "2" walkie-talkies, eventhough the 1985 Doc was sent to 1885, so there should be only 1 walkie-talkie, making it useless. But the 1985 Doc could have just left his walkie-talkie in the DeLorean for Marty and the 1955 Doc to find.
Marty is heard cocking the pistol. The Colt Peacemaker is a single action pistol, which means the hammer must be cocked back before each shot. Double action revolvers (which had not been invented in 1885) can be fired by only pulling the trigger, or first cocking the hammer back. We actually see Marty cocking the pistol back between every shot.
The walkie talkies Doc and Marty use while on the train, appear to have a Burgess dry cell battery strapped to them. Dry cells were not invented until 1886. In 1885 wet cells were available but typically fragile glass containers with lead rods hanging from the open top and needed careful handling to avoid spillage making them unpractical for mobility. It wasn't until 1896 that the first dry cell was developed for commercial use. The Burgess Battery Company was not founded until 1917. In actuality, The Doc from 1955 installs the Burgess batteries as indicated by the line "just in case, fresh batteries for your walkie talkies"
As the train carrying Clara is leaving the station, the rail underneath the locomotive drive wheels appears to be wet, causing the wheels to slip. However the rail could have been wet from the boiler's water tank. Or it could be oil on the rails, since the locomotive engineer puts oil on the moving parts of the wheels and drive mechanisms before leaving the station.
When trying to reach 88mph on the train, they unhook all of the wagons in order to loose weight, but they leave the firewood wagon which is the heaviest. They didn't need firewood because they used presto logs.
On the morning that Marty is suppose to have his shootout with Mad Dog, an automated machine in Doc Brown's shop makes breakfast. One part of the machine cracks some eggs and slides the frying pan over to an open fire. But as this happens, the eggs are pushed over too and you can see that some of the egg whites are already cooking, suggesting that the pan is already hot.
When Marty and Doc are standing by the railroad tracks at the ravine, it is evident that the railroad track is wildly uneven and radically steep, even by the standards of the day in 1865, and is clearly just prop track laid on rough ground. This is most obvious on the track in the foreground when we first see Clara on the runaway wagon. The roadbed would have required extensive grading and leveling before laying track in order to be usable.
The DeLorean Marty travels back from 1955 to 1885 in clearly has a lifted coil suspension upgrade to help it drive at high speeds over the rugged terrain. This type of vehicle upgrade, commonly used on 4x4's, would not be available in 1955.
In the beginning of the film when Doc wakes up and tries to remember what happened after the DeLorian time traveled, Marty scares him and he falls back onto his organ. This organ is actually a pump organ and requires air to fill via pedals to make a sound. Also the sound played is of a pipe organ. Pump organs make a more airy, reed type sound not the sound of a pipe.
As Marty travels to 1885, the Indian Tribe were only just a few feet away from him, but as he shifts into reverse they're further away. Because the DeLorean needs to go 88 MPH in order to travel through time, Marty would do what he was afraid to do: "Crash into the Indians" even if he were to slam on the brakes, he wouldn't stop in time.
When Doc and Marty hold up the train and one of the engineers disconnects from the train from the cars, Doc is pointing the guns at the engineers and they have their hands up. Then the engineer puts his down while Doc is pointing the gun at him and then puts them back up when Doc turns away with the gun.
When the final log blows in the locomotive, a close-up of the boiler shows rivets popping out and jets of water coming out of the holes. In all subsequent shots of the locomotive, all the rivets are still in place.
When Doc and Marty are first out at the unfinished trestle there is nothing on the trestle tracks but later when the engine is on the unfinished trestle after pushing the time machine, there is a cow catcher-like barrier at the very end of the trestle, which the engine hits. But when a front view of the falling engine is shown there is nothing on the front of the engine's cow catcher.
The headrest on the drivers side of Marty's pickup truck is missing when Biff opens the door for him toward the end of the movie, however when Marty is stopped at the intersection preparing to race Needles the headrest has reappeared.
As Clara's wagon goes over the cliff it rolls over sideways spilling some of the contents, but in the next shot the wagon is going over straight forward with the contents still in it until it almost hits the bottom.
When the train in 1985 is approaching the car, the shadow of the engine on the solid fence along the side of the tracks shows the engine is by itself but a couple of scenes later it is a full length freight train.
Right after the third log blows, in a long shot of the train from the side, you can see Clara's feet dangling from the train briefly, even though in the previous and subsequent shots, she is hanging upside down.
As the DeLorean time machine is being pushed by the locomotive, it smashes through a sign indicating the end of the track in 1/4 mile. At that point, the DeLorean's digital speedometer reads 80 mph. At this speed, the vehicles would reach the end of the track in about 11 seconds.
When the diesel locomotive, Sierra County Railroad S-6 #11, hits the DeLorean in 1985, the engineer doesn't stop the train, nor do any motorists seem to notice the accident (several are seen staring incredulously at the DeLorean as it passes by a nearby railroad crossing less than a minute before the DeLorean's destruction). Furthermore, Marty and Jennifer return to the scene roughly an hour later, yet no police/fire/EMS have apparently been alerted to what would have been a very serious accident.
During the film, Doc urges Marty to destroy the time machine once they return to 1985, as time traveling has caused enough trouble for them already (such as almost preventing George and Lorraine from meeting, Biff getting rich with the almanac, and Doc being sent to 1885). By the end, Doc seems to have forgotten this and made a habit of time traveling with his family. This is a running gag--Doc can't resist the temptations of time travel for long.
In Back to the Future Part II, it is mentioned that Marty's life was partially ruined by a car accident in which he raced his rival, Needles, and crashed into a Rolls Royce, whose driver sued Marty in court and therefore ruined his life. Back to the Future Part III, however, depicts the (avoided) accident in a completely different light: during the race, the Rolls Royce speeds through a STOP sign onto the main road, thus getting in Marty's way and causing the crash. While the courts would normally find someone who drove through a stop sign to be at fault, the original Marty was participating in an illegal activity (the street race) with gross disregard for the safety of himself and others. He can thereby be held at least partly accountable for any accidents that happen, especially so if bodily harm and/or death was the outcome.
In the final scene of the movie, the child playing Vern Brown makes a beckoning gesture with his hand, then points toward his crotch. It's with his right hand, just visible past Doc Brown. The boy was mimicking the unit director, who was directing the camera to pan then zoom.
The Boiler Temperature gauge in the time machine is not connected to the Locomotive. We can see this as the Locomotive approaches the time machine to begin pushing it. There should have been a hose running between the gauge and the boiler.
When Marty arrives back in 1985 and sees the freight train hurtling towards the DeLorean, the shadow of the approaching train initially reveals that only one locomotive is used for the approaching shots; the second locomotive and freight cars are not attached until right when the train smashes the DeLorean (and the shadows of the freight cars become visible at this point.)