When George Temple exits the church, his shadow is behind him on his right side. Moments later when he steps down, his shadow is behind him on his left side. And, a huge shadow from a building is shown in the street, but it disappears moments later as the men approach each other.
After dismounting his horse in front of the saloon, Dink Wells puts the saddlebag over his shoulder, but it is backward - with the straight edge closest to his neck and the "half-moon" cutout portion facing away. When he enters the saloon, the saddlebag is correctly positioned on his shoulder, but in the few seconds it takes him to tell the other two outlaws outside that "there's only a kid in here", the saddlebag is now in the middle of a table about 5 feet away.
Glenn Ford's pistol is already cocked while in his holster. A professional gunfighter would never do that because of the possibility it would go off as soon as it was touched.
In a street scene, tiny cars moving along a highway can be seen in the background. In another scene, power lines and a pole can be seen.
(at around 1h) When the posse is crossing the horizon, jet contrails are visible in the sky.
George Temple explains to the men in the bar how a real gunslinger wears his gun low so his hand rests on the butt. Then when he goes and gets his own gun and straps it on, it's riding high enough on his waist so that his fingertips can almost touch the bottom tip of the holster and his hand is below the butt of the gun.