Factual error: The Blackledges' car has a license plate that starts with 34. Montana uses the first two numbers on their plates to identify the county that the driver lives in. 34 is the number for Sheridan County which is in northeastern Montana where there are no mountains in sight, but the Blackledge ranch is set near the foothills of a mountain range as you would see in western Montana.
Factual error: George's truck has 25 (Sheridan) county plates. The family wagon has 34 (Madison) 544 miles apart.
Factual error: The movie is set in the 1960s, but the yellow Pyrex set (called Shenandoah) on the upper shelves in the kitchen wasn't manufactured until the 1980s.