One goof says that the Sand Creek Massacre was committed by militia, not regular us troops. The USA had and has several different armies at any one time and it is easy to confuse them. The perpetrators of the Sand Creek Massacre were not militia, and not regular army, but members of the first and second regiments of Colorado Volunteers.
The Sand Creek Massacre was against the Cheyenne people, not the Comanche. The Comanches would not know about it, or even if they did would not care as the Cheyenne were a separate culture, language and people.
One of the Goofs places Sand Creek in California. It is located in Colorado.
All of the horses in the film are clearly shod. Indian horses did not wear shoes as the Native people did have blacksmithing shops or farriers.
Several of the women firing muskets are shown cocking and attempting to fire them again. Muskets were single shot weapons, that require reloading and re-priming before they could be fired again. The "Indians" also do this revealing that no one apparently knew how to use muskets, which was just not a possibility.
The Audie Murphy character stays clean shaven throughout the film.
Many of the women are firing Winchester rifles that were not invented until about 10 years after this movie was said to take place.
Though the film takes place during the Civil War, all the soldiers wear post-war cavalry uniforms.
When the Commanche begin to storm into the fort, one of the defending women (clearly a stunt-woman) does an expertly performed Judo-style throw against one of them. This many decades before such an Eastern fighting style was known by anyone in Texas.
While the defenders are on the roof of the mission trying to hide from the Comanches, Bax (Kim Charney) is holding a single shot percussion cap rifle with the hammer cocked. He accidentally drops the gun and it goes off. But the hammer is still cocked and no smoke comes from the barrel. This would have been impossible.
The haircuts of the men reflect those of the 1950 stylings, rather than those of the 1860s. Several of the men have hair stylings that could have been performed with electric clippers and not the scissors and razors available at the time.
The movie made a big deal about being in Texas. Saquaro (pronounced suh-WAHR-oh) cacti are found only in the Sonoran Desert, which includes Arizona, Mexico, and California.
The closest "desert" in what is now Texas is actually hundreds of miles south of where Sand Creek is located in California. Not only would it have taken the Lt. Hewitt days (or weeks to get there, West Texas very lightly settled until well after the Civil War.
The only mountains of any consequence in Texas are in the western and Southwestern area of the state, near around El Paso and what is now Big Bend National Park. The terrain in Northern Texas, the setting of the film, is either flat or rolling plains, neither desert, nor particularly high in altitude. This shows that the film was NOT filmed in Texas.
Despite being shown walking and fighting in the bright Southwestern sunlight, almost none of the women are wearing bonnets. Since poor women in Old West could rarely afford hats, they would have wear bonnets or risk sunburn and blindness.