More of the "Outcrop" on a hill in Groton, MA (continued)

Here is the view down from the outcropHere is a view of top of the outcrop (here the stone wall becomes "rock pile"):Here are a couple of the better preserved piles: Here is a view of a lower outcrop with very minor piles. Finally, at the base of the main outcrop, was this pile consisting of a ring of rocks. It seemed that all the piles on the slope were visible if you were standing inside this circle, and I like the idea that this is a place to site and watch the near horizon at the top of the outcrop.I cannot resist trying to analyze this site a bit. What I mean by a "marker pile site" is that the piles appear to line up. Here is a overlay graphic to show how some of the piles here do line up.
Lines of piles are indicated by red line segments. There might be some other alignments here. So, in the end if I diagram where the piles occur on this outcrop it looks somewhat like this (the circle at the bottom shows the location of the ring of stone which might be a seat):
This is very similar to a sketch I did. [Click here]

So at this point I hope the phenomenon is adequately described. Now comes the hard part of guessing what these marker pile sites are for. They are an extremely common type of site and I claim all of these sites have a very similar purpose.