Plot hole: Immediately before the attack on Pony-That-Walks' village Capt. Brittles states that it's 12 minutes to midnight,and orders the attack. The attack is a surprise attack, yet all the warriors pile out of their tipi's fully clothed, painted and with their eagle feathers braided into their hair.
Factual error: In the very beginning of the movie, the narrator says, "Pony Express riders know that one more such attack (referring to the Custer Massacre) would mean a hundred years before another wagon train crosses the prairie." Then they show a Pony Express rider supposedly carrying the news. But the Custer massacre happened in June of 1876, and the Pony Express went out of business in 1861.
Character mistake: After running into Indians on his last patrol, Capt. Brittles orders Sgt. Tyree to head south and meet up with the (indicating singular) Paradise River Patrol. He is then to proceed at his best pace to meet up with Capt. Brittles at the stage station. Capt. Brittles states that he will approach the objective from the east. Sgt. Tyree is then shown riding off perpendicular to the unit's line of march. After a brief time lapse, the unit meets up with another patrol of soldiers that once again identifies itself as the Paradise River Patrol. This Paradise River Patrol joins up with the larger body of troops and continues toward the stage station. No sign of Sgt Tyree. Upon arriving at the stage station, Capt. Brittles meets up with Sgt. Tyree and another body of soldiers which is also identified as the Paradise River Patrol.
Factual error: It opens indicating that Custer is dead. Which would be June 25, 1876. They show a calendar showing a month starting with a Wednesday with 31 days. In 1876 only March started with a Wednesday and had 31 days. When Nathan Brittles is retiring, Olivia Dandridge is attempting to leave the fort before winter sets in, which doesn't fit March.