Hill east of Lovewell Pond - border between Dunstable MA and Nashua NH

I explored this area as part of a continued exploration that started at Horse Hill in Groton, moved northward to Hauk Swamp and Hound Meadow Hill, and still further north to Blanchard and Flatrock Hills (see here) in northern Dunstable. I found sites at those places. I was looking for continuation of the pattern of low rectangular rock piles that I first saw in numbers around Horse Hill. By the time I got to Flatrock Hill, that style of pile seemed to have played out. Not so! A little further north on the edge of Nashua, I found three of them about where the blue oval is on the above map.
First glimpse, a peaceful valley:

A couple of large but beaten down rock piles are visible on the far side. It has long been a reflex to explore the flanks of shallow valleys separating hills. 
Some details of the lower one, seen from opposite "corners". Facing uphill:

 Facing downhill:

I hope you can see why I call this "rectangular".
Here is larger pile, a few feet away, uphill:

And the view back downhill:

(Several well-worn paths through there show up as paler lines in the dead leaves. This is a popular hiking-biking area.)
Having found two piles, it was natural to look around nearby to see if there were any others. Up on the brow of the hill I see something a bit more shapeless under the dead leaves and debris: 

 But it is definitely part of the group.

 View back towards the previous piles.

A nice little group of three mounds, in scope of the same culture present from here back to Horse Hill. I hadn't seen any like this since the Falulah, a few weeks ago.

People still making piles there today, right next to the trail: