The Duck River, also called Big Duck or Barren Fork, once flowed through the abandoned river valley below. The larger fork eventually broke through part of Backbone Ridge across the valley, and in ancient geologic time this left the valley dry and shortened the run of the larger fork to its junction with the Little Duck River. The site demonstrates the powerful erosional force of water, because tremendous force is required to alter such deeply entrenched rivers. Early antiquarians called the feature a "moat" because it lay near the Old Stone Fort wall and they assumed the site was a true fort. A continuous trench dug at the foot of the slope below the wall and within the old river channel appears man-made and may have provided material for wall building or, like ditches at related enclosures, held ceremonial significance.