When Julia joins the crowd following Walz to the assay office, she flips the sign on the bakery door from 'Open' to 'Closed'. However, when she returns, the 'Closed' sign is on the inside of the door again.
In the final fight between Deputy Ray and Storm, Ray can be seen wearing gloves in some shots and not in others.
Dutch repeatedly fires his revolver at the bar's swing doors, with people crowding behind them, not causing any injuries but only minor damage to the wood. In reality, some of them would have penetrated the wood and caused injuries.
When the little girl fires 'Jacob Walz' rifle there is no recoil. A rifle of that bore would have knocked her on her wallet.
After killing all three at the site where the gold had been stashed, "Dutch" dumps all three bodies off the edge. Before the last body lands on the other two, the body on the left noticeably jerks.
When "Dutch" teases the little girl into firing his rifle, the rifle goes off before she pulls the trigger.
The rocks used by the Apaches to seal the mine are obviously fake.
In the scene where the Apaches attack the Spanish miners, one of the Apaches hurls a spear, hitting a miner. As the miner turns away and falls, you can briefly see light reflecting off of the guide-wire used to guide the prop spear to its target.