When Robert Horton sits "naked" in a washtub, taking a bath, the waistband of the swimsuit he's wearing is momentarily visible.
In the final scene (:59 when shown on TV), the wagon train is shown passing a barbed-wire fence. Such fences weren't used till the late 1880s.
Flint tells the doctor that the wagon train was already on its way to Johnsonville but he couldn't have known that as the decision to start rolling in the middle of the night was not made until after Flint had left for the town.