Around Oakmont High - Ashburnam/Westminster/Gardner

I parked on the connector road to the northern athletic field next to Oakmont High in Ashburnham. Had I not parked there I would surely have missed this site. But I stepped into the woods west of the field, directly into an interesting place. 
First I see a large platform integrated into the wall:

 

 Another view:

Turning the eye uphill, two large messy mounds are visible.

There are some interior details in these piles. Although mixture of large and smaller rocks is consistent with field clearing, the way the larger and smaller rocks are placed has structure. In field clearing there is a different kind of structure: the larger rocks will be in separate piles, covered with piles of smaller rocks.

Looking further up the slope...ooh...something still larger:

Here are some details of the large ple, also showing hints of structure:
(from above)

(from one side)

(upper corner)

 

(from below)

How about that?

Here are views back towards the first two mounds, playing field in the background:

Note the level spot where I am standing for this photo above. It is like a terrace.

Now let's cut diagonally up the hill (further north) to a bulge in the stone wall:

Note the discolored quartz in the wall at the left end of the curly dead branch. Looking at the wall in the other direction, it is not a normal wall. What is this ramp for?

Seen from above, this is a bit of a rectangular section:

Now we come to the last feature I want to mention, some sort of terrace or old road on the far side of this wall. I cannot remember if it a continuation of the terrace from the earlier views back towards the playing fields but, like it, this terrace follows the contour of the hill:

Out along it, one more rock pile:

Hmm. I see quartz and a bit of an outline.

(from below)