Low ground piles with white rocks, in the Billerica MA woods.

I headed west out of a warehouse parking lot, quickly through the fringe of pine saplings at the edge, and down into the woods. Pretty soon I was with the wildflowers, the gaywings and the violets and, stepping across a small brook, I finally got into a woodland I have been wanting to explore since last fall when gunfire scared me off (as it was hunting season). Going westward and scanning the faint slope down to the wetland at my left and to the high ground more to my right, I began to see a few faint traces of ceremonial structures: a boulder with a scatter of smaller rocks on top, a couple of isolated rock piles, a split-wedged rock further down closer to the water. I stopped to admire and video this split along with its surroundings [Click here].

It is typical to come up to a rock pile site and not quite believe it. First I saw a clustering of cobbles on the surface next to a slanted rock. Could they have slipped off? I did not believe it until I saw a next pile and then a next. The site consisted of several acres facing south and sloping gently towards a wetland. These were ground piles almost entirely covered with forest duff.
Some had a noticeable white rock - and you know what that means.
In the end there were 18 or more low piles built on the ground, seen here poking out from between the cinnamon ferns.There was one small seasonal brook and perhaps a more permanent one. I looked for more piles beyond these small watercourses, wondering if the rock piles would all be restricted to the first little bit of woods but, no, there were still some other piles beyond. Here is a look back eastward at the site; the wetland is to the right.
There were three piles visible when I took this picture.

I kept going west till I crossed another brook and got into the woods rising beyond, at which point it got to be all white pine saplings and no rocks. One thing I saw on that far side before that and still next to the brook was another split wedged rock. You can see the drill marks along the edge of the split (and that is a white trillium growing next to the wedge).
I have to comment that here no split went un-wedged. On this last one it looks like the rock was split in order to be wedged. (Someone is going to tell me this is how they supported the upper rock in anticipation of collecting it later.)

After this, I did not see anything more, so I turned around. On my way back, I was cutting across through the site I found earlier and saw a few more rock-on-rocks. Then I went back across the first wetland and out.