In a scene where Charlton Heston and Forrest Tucker mount their horses and take out their rifles the action is repeated when the camera cuts to a close up on them.
4 Indians are seen up on the rocks, yet only 3 are shown chasing the rider.
The founders of the Pony Express were not William Cody and James Butler Hickok but William H. Russell, William B. Waddell, and Alexander Majors. Hickok wasn't a rider for the Pony Express he only worked as a stockman
Charlton Heston is billed as 'Captain William Frank "Buffalo Bill" Cody. "Buffalo Bill"'s full name was William Frederick Cody.
Chief Yellow Hand's name is a mistranslation from the Cheyenne. His real name was Yellow Hair, which ironically was an Indian name for George Armstrong Custer.
Buffalo Bill says he sees a Winchester Rifle in a Army man's hands, Winchester was not founded until 1865 four years after the Express had stopped operations.
30 year old Charleton Hesston was far too well armed, too old and too tall to play Cody who was 15 when he rode for the pony express. The express riders were small and wiry went unarmed to save weight.
Even though a great distance was supposed to have been covered, the same relay stations are used in the initial ride regarding the federal slavery bill.
When Charlton Heston removes the saddle from his dead horse at the start of the movie, he removes it without undoing the buckle of the belt that runs underneath the horse. If the belt was unbuckled, the saddle and the rider would fall of the horse.
The setting of the film is the beginning of the Pony Express, which ran from 1860 to 1861. Yet the Californian secessionists who try to stop the Pony Express's first-ever delivery use dynamite, which was not invented until 1867.
The legendary duel between Yellow Hand and Buffalo Bill took place in 1876, sixteen years after the Pony Express was created.
The film is set in the 1860's, but the handguns all appear to be using Colt 45 Peacemakers, which weren't developed until the 1870's.
The Colt Revolvers were Model 1873. Hickok wore Colt 1851 Navy revolvers which were blackpowder fired by percussion caps.
After Cody boards the stage at the start of the movie, Rance pulls out a Remington Over And Under Derringer. But the Pony Express operated from 1860 to 1861 and the Remington Over And Under was not manufactured until starting in 1866.
In the final shootout between Cody and one of the main bad guys, the actor's reaction of getting shot doesn't match up with any gun being fired.
The 4 Indians are shown high up on a rock formation looking down on a valley when the rider goes through at full speed riding away from them. They are subsequently shown having overtaken the rider. This would not be possible due to the amount of time it would take them to come down off the rocks and get onto their horses.
When Rhonda Fleming's character is walking up the stairs in the hotel (at 26:50) the shadow from the boom mic can be seen on the walls.