Rock piles and headwaters of Mulpus Brook, Lunenburg, MA

I stepped off the road and went a few steps up along the side of a tributary to Mulpus Brook and saw this:
The brook trickled quietly and I thought I was in a rock pile site. This seemed even more true as I came to new rock piles:They looked more and more pile like:
But then I saw piles scattered around made from rocks of different sizes:And this nice one made from much larger rocks:
This kind of sorting suggests field clearing stages - first the largest rocks are removed then the smaller ones. The way piles were dropped around suggested they might correspond to wagonloads of rocks:Also this place, wet though it was, was on pretty level ground contguous with a more cleared area which could have been a field. So I cannot be sure. These might be "agrarian" non-ceremonial piles. I could get a better idea if I walked up other tributaries of Mulpus Brook, which I hope to do sometime in the future.