A small rock pile site in the Marlborough MA woods

I was exploring an area of Callahan State Forest that was mostly just empty oak and pine woods and was surprised to come across rock piles. There were six or so similar piles built up on rocks and, to one side, a larger broken down "platform" pile built in a faint gully. I imagined viewing the smaller piles from the platform. I took a few pictures, noticed the flat faces on some of the piles (which by the way were not in line with the platform), and went on to explore other parts of the woods. This is on the side of a little valley and, pretty much across the valley to the southwest and up on a higher shoulder there was a single much larger rock pile. It might have been visible from the first site marking a line of sight on the horizon.

Here are some panoramas from the first site. [I had a smudge on my lense so the pics are not very good]. These are all pictures of the main cluster of rock piles.Some pretty nice individual piles:That is pretty "flat faced". Someday I hope to understand sites like this. What is it for? I see sites with flat-faced piles so often.

Here are some views of the larger "platform":It was in a bit of a gully.

Another interesting feature was a larger boulder with smaller rocks leading up to it.
Look at the side view:
The state park marked trail goes right by this place. Recently people were piling rocks over there at the nearest place along the trail.
I often find recent little play rock piling on a trail near where there are real piles. Do the makers notice the older piles in the background?

Now let's go across the valley to the south and look at that single larger pile. Here is a first view:
Here are other views. I was quite taken with the pile although I could not convince myself it wasn't a field clearing pile. It was in otherwise open pine woods with few rocks in general. A stone wall nearby and this could well have been a plowed field. Still it is nice to find a large pile and I think there are hints of damaged structure here:
Not to put too much weight on it but: this simply does not look like a field clearing pile. I would like to think this pile is not really isolated and is visible from the first rock pile site across the valley - it is only a hundred yards or so.