There is a collection of at least 27 rock cairns found along a bluff in an area of about 3 acres on the property. Their origin and purpose remains a mystery, despite examination by three archaeologists and numerous curious lay folks.
A blog at Mystery Cairns reveals all that we know about these features, which is probably TMI for most people. Any theories that might occur to readers will be most welcome by the BMF management.
Below is the largest, by volume, of the 27 identified piles. In the right background is another of the larger cairns.