Sites (in blue) with chambered rectangular mounds are pretty common along the headwaters of Falulah Brook in northern Fitchburg. I am sure there are others I have not seen. Sites (in yellow) with arrays of triangular piles are also pretty common along the old Mayo Rd.
Today I got thoroughly lost and so, when I finally stumbled on the type of site I was looking for, I had no idea where it was. Given where I exited the woods onto the road, I can guess roughly where the site was. But the ?s reflect my uncertainty.