Factual error: The boys go deer hunting somewhere in the Appalachians, but the geology is all wrong. That scene is in North Cascades National Park in Washington State. In addition, the "deer" they are hunting is a Red Stag. Not typically found in the Appalachians.
Revealing mistake: In one of the river flooding scenes after the dam bursts, you can see a modern day vehicle (most likely a pickup truck) for a few seconds on a highway next to the river. (01:50:30)
Revealing mistake: During the fight after Witty has been killed, Peiter throws a grenade that lands in a bush on the right of the path up which the enemy are advancing. However, the resulting explosion comes from the centre of the path and not as far away as the grenade flew.