Spruce Swamp Brook - Linear stone mounds along a brook in Shirley

Let me now get to the meat of what was interesting on my walk at the Holden Rd Conservation Land in Shirley. A few steps after finding that first pile, I thought I saw a stone wall off to the side of the trail and went to have a look. The "wall" turned out to be some exposed rock in an artificial berm about 40 feet long with a conical mound at one end.
I took pictures as best I could in the bright light.

After a while, I noticed some auxiliary piles and little notched dimple made from larger rocks on the far side of the mound. Something like this (birds-eye and profile):

Here is a picture looking down the berm towards the mound. In the foreground is a smaller pile with a bit of quartz:

 

 Here we are looking from the other end, towards the mound:

The "notch" is behind the tree. Here is a better picture, with the berm now visible off the the right:

Finally, here is the back side of the berm. You can see it is a big structure.

The auxiliary piles were hard to photograph. Here is one that is almost part of the berm:

 

And another:

 

So I contented myself with the flowers:

 closer:

 One more auxiliary:

After seeing this unusual linear "mound" I continued along the same ridge of land, and a few feet later it became a composite of trenches, hollows, and piles...until I got to the mound next to the wall I wrote about yesterday. Essentially, as soon as you step into the woods on that conservation land trail, there is a non-stop site to your right. 
After that I walked west, saw other structures [I'll tell you about later], and circled south and back east till I got back to the brook-maybe 1/4 mile south of where I was before. Here there were even more substantial man-made berms along the side of the brook. Were they just from field clearing? These are big tiers in two levels above the brook:

Seen from above, the berm rises above the level of the ground level:

 Actually, a couple of separate berms in one place:

So that is it. These linear structures are not so common and a bit peculiar. I hesitate to compare them to other things but field clearing does not create structure above the level of the ground like this. Reminds me a bit of Blood Hill. The strategy of following the Devens stone wall map, the strategy of trying to squeeze some ceremonial sites out of that sandy region along the Nashua River - payed off. And it is telling me I should go look at Benjamin Hill next.
Update: A bit more about this site, later, here.