Brown Road Conservation Land Harvard

There is a trail into the woods to the north of Brown Rd. in Harvard, at the lower curve of the road. If you go in there and stay to the right you get down into the wetter area. Just beyond is a little knoll that looks inviting. I thought it would be worth looking on the southern side of this knoll, almost in someone's backyard but facing outward towards the main view there. Sure enough there was a small site. There are about five structures in this picture:
Here is a detail of one of the rock-on-rocks to the rear:
You can see there are actually more piles here than at first glance, buried under the leaves. Here is a last one: