Revealing mistake: In the scene right after they leave Scar's wigwam, when Ethan and Martin are speaking to each other around their camp you are able to see a small brown dot right above the sandy hills. This dot is the character Debbie's head while she is waiting for her cue before she runs in to the scene.
Continuity mistake: After the fight between Martin and Charlie just before the wedding both fighters get extremely dusty and dirty. Then Mose appears after escaping from the Indians. While the rangers and searchers gather to hear Mose, Martin and Charlie are now in clean clothes and appear to be freshly showered.
Continuity mistake: When Laurie is reading the first letter from Martin, Charlie McCorry is sitting in the chair opposite her lightly strumming his guitar. The camera angle is facing him showing his fingers are wrapped around the fingerboard. As she keeps reading, the camera angle moves to behind his head and now showing Laurie's face. In the left side of the scene, Charlie's fingers are now on the side of his face slightly under the chin and his elbow is on top of the fingerboard. When the camera angle goes back to looking at Charlie, his hand is once again around the neck of the guitar.
Continuity mistake: In the scene where they find the massacred cattle, Ethan tells Martin that the horses need grain and rest. Ethan and Mose ride by Martin in the next scene and Martin, whose horse is dead, tries to get a ride with Mose. Despite the fact that Mose and Ethan have horses that are galloping quickly, Martin arrives at the burning house the same time as them.