When Blayde Hollister shoots Bryant Marlowe, it occurs at night in the dark, but the very next scene as Hollister begins chasing Will Marlow almost immediately, it's day time.
While Tonia plays the piano, Hollister heads for a armchair and sits down ostensibly with the cigar in his mouth. Subsequently he is shown finishing to sit with the cigar in his right hand.
There is a clear difference between Wild Bill Hickock's shoulder length hair and actor Reed Hadley's real hair.
When Bryant Marlow and his gang are chasing Blayde Hollister (Gary Cooper), they shoot at him and shot appear to hit the hillside next to him. But one of the shot impacts sends up a smoke ring from the charge planted in the hill, showing that the shot impacts are only special effects charges.
Each time characters shoot at a can to demonstrate their marksmanship, there is a slight delay between the gunshots and the can's movement. In reality, there would be an almost instantaneous reaction.
When Hollister stops to inspect hoof prints when pursuing Marlow to Fort Worth, the road behind him shows obvious signs of being mechanically graded e.g. by a bulldozer.
In some shots of chases along dirt roads, tracks made by pneumatic tires are visible.
When Blayde Hollister mounts his horse to ride to the Robles compound near the end of the film, the sound of a horse galloping can be heard several seconds before he begins to move. There are no other horses moving in the street and the sound doesn't change once Blayde begins to ride.
When the Mexican riders approach a sign post right at the start of the film, the signs say Austin in 315 miles away and Dallas 12 miles. In reality, the distance between the two cities is 195 miles...not 327.
As the new marshal rides into the Robles ranch outside Dallas, there are low mountains in the background. No such mountains exist near Dallas.