Boston-Maine Railtrail, Mason NH Part B

Continuing from here. We walked out of the woods back to the rail trail, went further north and looked at a massive wall next to and below the rail trail. It was at "B" on the map, actually the top of a watershed leading to Mason Brook.
Looking down from above:

Here we are looking at the well made end of the "wall". Looking back towards the railroad bed above:

Some panoramas:

 I was commenting that there is a lot of internal structure in this "wall".

Meaning: nooks, crannies and well built faces in the middle of the wall, not at the edges. For example:

 closer:

Last look (the railroad bed is the higher ground behind):

I don't believe for a second that that is a colonial wall for any of the usual agrarian reasons. 

Suspicious, we explored the vicinity carefully....oop! here is a small pile and then something bigger in the distance (about 40 yards from the "wall"):

This is a large trench in a pile, at the end of a regular wall:

I have seen trenches like that before, eg in Estabrook Woods and on Mt Elam. I interpret them as mass burials representing something quite different from the individual piles with hollows, seen up hill to the south (around "A").
Closeup of the trench:

A nearby pile with quartz:

And a low pile connecting the trench to the end of the regular wall:

All of which says this is not just a collection of walls.