Roadside Attractions - Bush Hill Rd, Pelham NH

Driving somewhere on Bush Hill Rd (I think near the blue outline above) I noticed what looked like a very fine "cairn" down in the woods below the road. On closer inspection it was a modest pile built up on a vertical-sided boulder.I parked and got out to take a few pictures. There were two other similar piles more or less the same distance as the first from the road:
andThe whole area was on a sort of plateau, or shelf, on the steeper hillside below the road. The shelf was enclosed by stone walls. Here is a view back towards the road.
The first and second pile are center and right. The third pile is to the upper left.

Off to one side, was a big and very messy pile of smaller rocks, that might have been a viewing platform, or a field clearing pile - except there was no nearby field and other field clearing characteristics were missing. Sorry for the poor focus, take a close look at this picture. Among other things you see a cascade of rocks spilling over the edge of the shelf. At the left edge of the picture, midway between top and bottom, is a darker shadow, which is a crevice in the bedrock. The smaller rocks in the cascade seemed to have been pulled out from the overall pile and seemed to have been tossed to the side around this crevice; as if someone had removed the smaller rocks from there. Why would someone dig down into the pile this way?

Let me comment that this site is quite like the one from Sherbourne from last week: it consists of a few large vertical sided piles, somewhat in a line, on a level spot, enclosed by a wall. I believe these are one kind of marker pile site.

Let's have a last look at the first and second piles:Update: In comments, Larry asks if the second pile has a manitou stone on it. Here is better look at the 2nd pile with the large rock on the right: