Large Mounds at College Rock

With reference to previous posts (here, here, and here), I was hoping to understand all the incredible variety of structures at College Rock by seeing them in the context which, by now, is familiar to me: a context of structures in and around large mounds with hollows. Aside from one such mound built into the stone wall next to Beaver Brook, I did not see anything comparable until I got far enough south and west - where I saw this one:

And as I gazed into the woods...lo another mound was looming:

On closer look, the wall on the side of the hollow is unbelievably well preserved:

closer:

I was walking along here, when I noticed some even larger mounds in the background.

Or were they stone wall? Then followed a sequence of higher and higher tiers of stone mounds. In pictures: Mound#1 with mound#2 in the background:

Here is mound#2, which is built into a wall. I am not sure mound #3 is visible behind.

Here is mound#3:

Let's take a closer look:

It's a long thin eyebrow of a rock pile, with a notch in it. Some other views:

You can see the stone walls going crazy in the background.

(Where have I seen a long thin pile with a notch in it before? Well I think Pratt Hill had one. I saw one at Tenney Rd in Westford). 

Messy as it was, mound#1 is worth a closer look:

 It is a slightly different layout.

Stone walls with mounds in them (or predating them) seem to have been a habit around here. One more, on the way out:

Goodbye for now: