Factual error: When the boy is crying because he's made to ride a pony, the Texas flag is made wrong. The top star point is toward the red stripe instead of the white strip as it should be. In other scenes the flag is flown upside down - the white stripe should be on top.
Factual error: The movie takes place in the early 20th century (1910s or 1920s or so). When Dean and Jerry are riding in a RR cattle car with its doors open you can clearly see parked automobiles from the 1950s through the open door of the train car.
Factual error: The movie's beginning takes place in 1868, yet all the men pack cartridge Peacemaker Colts (not available until 1873) and model 1892 Winchesters (not available unti 1892).
Factual error: Two grave markers at the end, approximately one hour and 27 minutes into the film, have the date of November 7, 1889, on them. The script made it clear that the climactic gunfight between Glenn Ford and Broderick Crawford came on a Sunday. Ford was called out of church services, for example. According to The World Almanac and Book of Facts, November 7, 1889, was a Thursday, not a Sunday.
Factual error: During the balloon ride the Basilica of the Sacred Heart of Paris is seen. It began to be built in 1875, 3 years after the date the movie is set.