I took this photo this afternoon in Opacum Woods
I was on the Northwest Corner of the Opacum pond, about where the O in Opacum pond is on the trail map This Structure of 3 built walls against the side of a large rock was interesting. It may have been a building, or a foundation? There was a spring in the ground nearby with built walls lining it in a circular patter and the top was covered by three or four rocks. I only had my cell phone with me, as I was CC Skiing on the pond. The satellite photos for this area just aren't as good as east of here yet.
Anyway, I am going to head back there next weekend with a real camera. There are other interesting rock things on the south west of this pond, near where the "rock shelter" as seen on the website is located.