Northern Wrentham State Forest

I was told there were some interesting sites in the northern part of Wrentham State Forest. Having been there four times without seeing anything, I am starting to wonder what am I missing. Maybe a little further north? This last time was east of Taunton Str., north of the highway. A couple things:

A nice example of a stone 'U'. 

Over on the eastern side, a familiar site, slightly rectangular with a hollow:

This was part of a larger structure, shown on the left here:

It was by itself.

Back over on the western side, a few hundred yards from the road. Is that a rock pile?

Yes it is.

Pretty faint: