Another lobe of a favorite site in Tyngsboro

As I was driving along, approaching this little pond on the right I noticed a lot of stone work to my right and stopped to take a look. Eventually I found some great piles but before I even walked in there I noticed something interesting on the other, downhill, side of the road. Someone build some little staircases down from the road and from the adjoining property, leading down to the brook that flows off downhill there. I am convinced there was some kind of mill in this area because there was also a trench diagonally off to the side of the brookA few feet below these steps was a trench that looked like a mill race. If this wasn't private property with parking obviously in-appropriate, I would like to sneak down this brook to see how it fits with the major site below. There must be more piles along the brook.
Anyway I went back to the up-hill side of the road and took some quick pictures. I was made nervous by my camera being more and more broken - this time I could not turn off the flash. At the same time I was nervous to be easily visible from the road and also on private property. So I took a picture or two and started to sense something larger looming in the distance, which you see faintly on the upper right of this panorama. For reference, here the brook is to the left and the open space beyond corresponds to the little pond in there.
So I rushed around taking pictures. First here is that large pile seen from different sides:
And here is a view down towards piles below:
Notice the brook at the bottom. The pond is to the right in this photo. So from this knoll we have a fine view out to the southwest and a nice view out to the west across the little pond.

There also numerous piles along the brook but most were decrepit. Here is a nice one:
In this picture, we are looking back towards the road with the brook to the right.

On the other side of the brook the ground rises slightly, as is not shown on the topo fragment, and there are a few piles over there which I saw before - I think it was last winter I dragged Barb and Joe on a hike up here and stopped briefly to get pics of these piles. I was impressed, at the time, with this pile wrapped around a boulder:I also photo'ed a pile in the middle of the brook. It was in line with a stone wall coming downhill and I was wondering about dams and mills. There were several stone and dirt walls running down to the brook and there were lots of destroyed structures which could have been piles or something else. It is a very complicated collection of structures in there with what I would guess is a complex history. Some of the piles look pretty new and also those steps look pretty new. But there are lots of broken down things all around as well. Then how about this: last winter I thought I saw a rock pile on a cement culvert. This time I wanted to make sure so I climbed on the stone wall leading over to it and got this picture:
So what the heck is up with that? I get a feeling of someone recently fooling around with these rocks. This cannot be more than about 50 years old. I suspect the wonderful pile-gap-pile site downstream aways is built by the same more recent person. So my final guess: an old broken down mill with a modern Indian re-using the stones for piles. The site might have been ceremonial before and after the mill. The ceremonial mixed with the profane.

If you go downstream from this site there is another very nicely preserved site. This makes it likely the area has recently built structures.