These are from an area of an acre or so containing four good sized stone mounds and several others in different states of disrepair, and with numerous adjacent smaller piles. There were "Manitou" stones, quartz highlights, and other interesting features but I want to concentrate on careful comparison of the structure of three of the largest best preserved of the mounds.
Let's start with a sketch and then back it up with some photos:
Each example has two chambers, and two have retaining wall on the inner side of a collapsed portion, suggesting either a deliberate ramp or an "annex" added on to the side of the larger structure. In any case, you can see these are very similar.
Here is a view of "Mound A", from lower down but at the same angle as the sketch above. Note the flat sides, and the bit of vertical wall.
Another picture shows the two inner chambers:Note these are also rectangular. But the sides were not lined up with the sides of the mound.
Here is a video of "Mound B"
At the beginning, I am standing at the top of the collapsed portion, looking towards the back, then along the side, then down into quite deep (~5') craters on the inside of the mound. I am not sure if it was one big crater or two separate ones. Aside from that, this is very similar to Mound A. Here the inner chambers are rectangular with sides that do line up with the sides of the mound.
Here are some photos of "Mound C". I tried to get a panorama of the opposite (downhill) side from the collapsed chambers [click here] but it is a bit hard to get the whole outline from this picture. Here is a view of the top:You can sort of make out two hollows on the left side. Here is another attempt to photo it, with lines superposed to show where I see hollows:
I believe one of the strongest arguments in favor of these being Native American mounds is the uniformity of these details, implying a uniformity of intent - an intent which is far from anything ever held by the Anglo-European cultures. Europeans have no culture of creating truncated, rectangular, pyramids, with inner chambers. And yet here, in northern Fitchburg, some culture did.