When Virgil and Everett first approach Bragg's men in the saloon, the cowboys are relieving themselves at the bar's "piss trough." Virgil demands that they "button up." After the shooting is over, when the bodies are shown on the floor, there is no trough or any sign of wetness in that area.
When Bragg comes out to confront Jack Bell in the opening sequence, he hands a cup to one of his ranch hands. After the shooting, the cup is not seen again.
When Everett and Virgil are agreeing to protect Appaloosa, the lighting in the room changes drastically between close-ups and wide shots. For the close-up of Abner Raines, the curtain is open, lighting his face with sunlight, but in the wide shot the curtain is closed.
When Alison and Virgil are in the coffee shop, she orders a coffee and a biscuit. Although refused a biscuit at first until Virgil intervenes, she is actually served a soup and bread roll, which moves around as the scene unfolds. Everett also receives a coffee at the same time, though no coffee has been ordered for him.
During the opening murder scene, the cocking lever of the Winchester is fully down (probably a jammed blank didn't eject). There's a cutaway and then while Bragg is still walking away, we clearly see the rifle with the cocking lever is now fully retracted.
When Virgil and Everett are in the hotel and Virgil is smoking a cigar, it is not lit. He inhales a few times and never exhales smoke.
In the hotel dining room at breakfast there is a stainless steel coffee pot on the table. This is set in an area of abundant silver mining and would have been made by a local artisan out of silver or just plain tin that was plated with porcelain or silver.
The framing of the house being built appears to modern construction, using modern lumber, not the rough cut lumber of the day. It also appears to be double wall construction, not the single wall type of the era.
When Everett takes one of the horses up a draw to confront the Indians who are stalking their party, he gives the extra horse to one of the Indians. Over his right shoulder in the near-distance is a graded road (mine access?) which is much too evenly maintained to have been from the late 1800's.
(at around 1:35:00) When Virgil and Everett are talking on the bench a moving camera can be seen reflected in the window pane above Virgil's left shoulder.
When Joe Whitfield approaches Virgil Cole and Everett Hitch the first time in the hotel dining room - shortly into their conversation you can see the numbers "191" flash momentarily in the upper right hand corner.
When Virgil and Everett are taking Randall Bragg back to town, some crew and a moving camera can be seen reflected in the window.
The sign outside the Marshal's office is incorrectly spelled "Marshall." Although homophones, the family surname Marshall is normally spelled with two L's, while the public office Marshal is only ever spelled with one L.
A store in town (seen when Bragg is brought to town in captivity) is called "Ladies and Gents Clothing and *Millinary*," should be "Millinery."