I was leaving the place just mentioned and had gone no more than a few hundred yards from where I had parked when I noticed some more rock piles right next to the road. A small site like this would be barely worth mentioning except that there were a couple of examples of probable "pile-gap-pile" arrangements. So I wanted to show these.
Here is one:and here, perhaps, is another:A problem is that once you start imagining that you are seeing these then every rock next to a rock pile becomes suspect.
There are only two other sites I know that have multiple examples of this kind of structure. One is called "Above the Falls" and the other was in Westford/Tyngsborough. These are all very water- related places. For lack of better phrase I call them "pile-gap-pile" and imagine them as gateways, where the piles define so-called "negative space". For other references see here. As I look over old examples, I am surprised that I saw them in so many different places, I thought they were more rare.