Wend Con kills the man in the red rock cliffs, he is still breathing when Doc Shabitt and his gang find him, he is still breathing.
Toward the end, when Duncan shoots and kills Doc Shabbitt, Doc is still breathing.
In the opening minutes the family's wagon is shown with a spare wheel attached to the front of the wagon. Seconds later as the wagon proceeds there is no spare. It magically reappears later.
When Susanna fights off Red with the club in the middle of the night you can see that the club is rubber because it flexes as she hits him with it.
A log cabin in the mountain wilderness in the late 1870s would not have had glass panes in the windows.
According to the Merriam-Webster online dictionary, the first known use of the term "rug rat" was not until 1975.
When Red goes off by himself to check out the McKaskels camp he is told by Doc that if they hear a shot they would know he" bought the farm". Bought the farm is an expression that was not used until WW1.
The date carved in the cabin by Susanna's brother is September 1876. Earlier in the movie, she learned that he was killed with Custer at the Little Bighorn, which occurred in late June of that year.
When Susanna, showing pictures to Con and speaking in 1876, says her brother is at Fort Kearny in the Bighorn Mountains, that Fort, Phil Kearny in Wyoming, had been abandoned for eight years due to the Treaty of Fort Laramie in 1868.
Since her brother was under Custer, in the 7th Cavalry, he would have been stationed at Fort Abraham Lincoln in Dakota Territory in 1876.