Watertower Hill at the old Metropolitan Hospital Grounds in Waltham

I walked in along a road on the north side of the hill and cut up into the woods to my right as soon as there was a bit of slope and a sense of outcrops up that way. I came across a rock pile in the ferns and, not quite believing it, took several minutes to find other piles nearby. They seemed to lie in two lines joined at a corner in a pattern something like this:
where the gray outline is a hole in the ground and the black square is a boulder. Here is a picture of the hole:I am not sure if the hole was in line or not. I think it was tangent to the line.

Lined up like this, these piles might be what I call "marker piles"Here is a detail of the far pile:
A few others along the same line:
It is a stretch to see these piles having one vertical side (a feature associated to marker piles) but it is not impossible. The piles are well defined but pretty beat up.

Just up hill was a place of tumbled boulders in the kind of dis-array that I think of as a biproduct of practical activity. As if they had been tumbled down to here from some disturbance above.It is as though the boulders were dumped down almost on top of a rock pile site. Which sounds implausible.

So perhaps someone can go back and give the place more study. It seems that exploring, in the suburbs of Middlesex County MA, ambiguous sites should be expected.

Update:
I should mention that these rock piles are on the northeast side of the hill.