Went out to explore near Parker Hill Fitchburg, including taking pictures of some mounds I found before when I did not have a camera [see here]. Here is the scene I described then:
It looked as I remembered - those gray spots on the hill below the power lines. But for some reason, having a camera got me to look more carefully and I cannot convince myself that these are ceremonial rock piles. Closer:
There was a nearby field and there were larger rocks strewn around. So I'll subtract this site from the maps. (The lowest left blue outline here).