When and Where?
If it was a documentary about a historical event the time and the place would be clear, but She Wore a Yellow Ribbon happens more in the Wild West of imagination than in real history.
Custer's Last Stand happened on June 25, 1876 in real history, and the date is mentioned in a few movies also. She wore a Yellow Ribbon opens with mention of Custer's Last Stand. Cheyenne Dog Soldiers who participated have come south trying to incite the Kiowas of Pony-That-Walks into joining the war. The garrison at Fort Starke receive details of the casualties at the Little Bighorn.
And Captain Brittles marks off the day on a monthly calendar several times. The month is not marked, but 1876 is the year.
The garrison is stationed at Fort Starke. James Warner Bellah wrote a series of cavalry stories set at the fictional Fort Starke, which had a rather vague location. Four movies were adapted from those stories set at Fort Starke.
Fort Apache (1948) involves members of an unspecified cavalry regiment. I like to think that it is the 13th Cavalry, but since it is commanded by Lt. Col. Kirby York at the end and the 2nd Cavalry is commanded by Lt. Col. Kirby Yorke in Rio Grande (1950) it might be the 2nd Cavalry. They are stationed at a fictional Fort Apache, no doubt within a few hundred miles of the location of the real Fort Apache, Arizona. She Wore A Yellow Ribbon (1949) involves members of the 2nd Cavalry (at least their caps have a 2) at Fort Starke in or near Kiowa territory & near the fictional Paradise River, & south of Sioux territory. Rio Grande (1950) involves members of the 2nd Cavalry (at least their caps have a 2) at what might be another Fort Starke or Stark, probably not in Texas, and a few days' ride from the Rio Grande and a few day's ride from Fort Bliss, Texas.
And The Command (1954), is probably set in 1876 since the local Indians - listed as Cheyenne, Arapaho, Sac, Fox, Omaha (or Otoe), and Pawnee - are stirred up by news of Custer's Last Stand. In The Command (1954) a 2nd (or 7th) Cavalry company is returning to Fort Starke when ordered to help guard a joint army/civilian wagon train travelling from the town of Cashmans to the Paradise River, to reach the army of General Crook, Cook, or Hook. In the original story they were riding to reinforce the army of General Crook after the Little Bighorn.
The vague location of Fort Starke in The Command (1954) seems to fit with the vague location of Fort Starke in She Wore a Yellow Ribbon (1949).