When Preston is in jail, sitting up against the wall of his cell, the bricks behind him are peeling away from the wall. As bricks do not "peel" it is obvious that this wall is not a brick wall but a wall with a brick pattern wall paper.
When the woman is being used as a shield at the film's beginning, the closeup of Sheriff Biggs pistol shows no bullets in the chambers, but after she yells for him to shoot, the next closeup shows one shell, a hollow point, in the cylinder. Hollow points had not been invented yet.
Shortly before the revenge-seeking riders catch up to the wagon, radial tire tracks are clearly visible in the dust of the road.