Rock Ledge. They (I don't know this "They") have found proof that old timey folks (read: Natives) used to use this ledge as a home. Well, sure...until it would flood...walls like that ain't just formed because of nothing.
Yay for "Fecal Contamination Present. STAY OUT OF THE WATER!" Ross tells me that the mill is on the other side of the river, so we didn't get to see it. Damn.