Factual error: Despite taking a three-day trek across the blazing Arizona desert with no food, water or provisions (and definitely no knives or razors), neither John nor Manolito grows a beard, or even any stubble. They both arrive in Nevermore perfectly clean shaven.
Factual error: The Apache spearhead Buck appropriates is very obviously made from machine-tooled steel. Indian tribes in 1870s Arizona made their weapons points from hand-knapped stone and on rare occasions, iron. They never developed steel-making technology.
