In the fight scene near the end of movie, Kirk D's hat is on, then off, then on again in a continuing sequence.
The name of the ranch is the Triangle, but the branding iron is in the shape of a circle.
When Dempsey Rae (Kirk Douglas) drops off the barbed-wire wrapped bad guy Concho Perez (Mark Hanna), he pulls Concho off his horse and Concho lands on the barbed wire and yelps in pain. Then Jeff Jimson (William Campbell) picks up Concho to unwrap the barbed wire, but the wire has no barbs on it, just smoother twisted strands of wire.
When Dempsey Rae and Jeff Jimson are rousted off the train near the beginning of the movie, they are standing in front of a boxcar that has a registration mark painted on the side indicating it was built in December 1923. However, the movie is set in the old West of the late 19th century.
At the end of the movie the stampede is stopped by a barbed wire fence. The fence posts are obviously added later in production. That scene has been used in other horse operas, too.
The train shows much evidence of twentieth century construction. The locomotive has a steel cab, as well as cylinder valves and valve gear of a design not available until the early 1900s. The cars all have steel underframes and more modern-style trucks.