During the fight between Willett Gashade and Billy Spear Billy's hat on the ground behind them alternates between being upside down originally and then right side up later. The canteen between the fighters and the hat also disappears in the final shots when the fight ends.
When the woman and Billy ride up on Gashade after spotting the man alone, there are more fresh tracks in the sand than just the three would have made. And, when the trio rides off, there are already fresh tracks in the sand as if they were doing another take.
Within the first two minutes a bag of something white, perhaps rice, is punctured so it will trickle out and leave a trail of white on the ground. Then the horse's hooves are shown in close-up walking along beside the white trail. Both before and after that, in wide shots the horse is seen walking in front of the mule which is carrying the trickling rice. So the horse could not be walking beside the trail of white.
When Willett takes Coley's pistol he puts it in his own empty holster. The holster is too big and the pistol sinks way down in it. Later Willett is shown walking and the pistol is higher, in a normal position.