Other mistake: At the very end, when a man is painting the "F" of the city's new name on the water tower, with white paint, you can see that though the brush is white, and it is touching the surface of the water tower, no paint is left on the surface of the water tower. Nevertheless, the painter continues painting the letter in the next shot, even though no paint is left on the surface.
Factual error: In the scene where the people of Rejection/Perfection are preparing to fight the Dirt Dragons, Hereim loads the Punt Gun and puts a little gold piece in it (a percussion cap, containing a small amount of gunpowder used to set off the main charge in the barrel). He shoots at the Dragon when it pops up and misses. The next time he loads the gun, he does not replace the percussion cap (which can only be used once), yet he is still able to fire the gun with no problem and kill the Dirt Dragon.
Continuity mistake: When Hiram, Juan and Kelly first see Old Fred's wagon in the distance, the white tarp on it is draped across it and down one side. When they arrive at it, it's draped differently. They also arrive at it from the side, when they were approaching from straight in front on it.
Factual error: In the muling station, Juan is at the telegraph when a Graboid comes up from underneath him. As he is flung up into the air, he 'hangs' there for just enough time to disprove the law of gravity. Also when the Graboid breaks through the floor, it is just behind Juan, which would have sent him forward (over the telegraph) - yet he is thrown backward.
Revealing mistake: When Hiram, Juan and the boys are camping out on their way to the mine, one of the cowboys is hit by a couple of Dirt Dragons (one from either side) as he runs to the others. His body is tossed one way, then the other (as they hit him), but then sort of 'jerks up' against gravity, indicating he is being lifted by a wire.
Continuity mistake: When the Dirt Dragons show up at the muling station, after the trio shoots at them, Kelly is emptying his gun of the used cartridges, but then they turn to shoot it behind them - Kelly doesn't reload, but is shooting. There's only about 2 seconds for Kelly to open his jacket, pull out more bullets, load the gun and fire - not enough time.