Stone Walls, Squannacook Hill - Shirely MA

I have been trying to get in to this hill for a while. Finally figured out how to get in there but I did not see much except the stone walls that I had expected based on the old Fort Devens Topo map (click here).
Saw this short stretch.
But then it turned out to be lined up with a more extended wall a few hundred yards away, as if a separate section. Here is this more extended wall: