Outcrop and Rock Piles (2) - Northborough MA

I was walking in Northborough and came to a nice outcrop with rock piles (see video here), in a more or less south-facing layout. Here is the complete outcrop:
A sketch of the same scene helps to see where the rock piles are (highlighted by the red dots):Most of the rock piles are on support rocks and there is a rounded bump of outcrop at the top of the site. Note how the piles fill the view, evenly dispersed. Note how they almost suggest a checkerboard.

Here is the view from a different angle, a bit to the right and closer:
Let's take a closer look at the pile at the lower left in the last picture:That vertical-sided, wedge shape fits the idea of a "marker" pile, and the even spacing and arrangement of the pile in approximate lines re-enforces the idea this is a calendar site.

The outcrop is along the side of a shallow valley and I could see some rock piles over towards the bottom and on the other side of this valley. Here, we are looking back at the outcrop from one of them:
Here is the one on the other side of the valley.A couple of other views of the main site. Here is one from part way up, looking back down the front of the slope and out towards the valley with those outliers off to the right.
Note the lighter colored stone, which is feldspar - the poor man's quartz.

Here is a view from the top. We are looking down the front of the slope, southwards:
As you can see, there is another smaller outcrop off in that direction and lots of other rocks sticking up as bumps in the forest floor.