Indian Graveyards - Concord, MA

There are three similar sites in Concord that I think of as "graveyards". Of course I have no idea if that is correct, if anything is to be found under the piles. So what I mean is: rock piles sites with 12 or so low-to-the-ground circular rock piles, each having a bit of white rock. Here are two of the larger such sites I found in Concord.

First site
This one is somewhere in Estabrook Woods. I have shown it to the most knowledgeable Estabrook experts and they did not know about it. I think Thoreau missed it. On approach:
See that pile on a rock in the rear? It is not a ground pile and not, I think, a grave. Here is a closeup from one side:The pointed rock in the middle, facing you, is symmetrically placed. FFC thinks that pointed rock is the head of a crow effigy.

Here is one of the "graves", completely non-descript but, believe it or not, most of these piles incorporate a white rock:The site is in a space between a triangle of stone walls. The crow at one corner, a completely damaged pile supported on a rock at another, and a collection four turtle-like piles in the last corner. So, here are all four "turtles":Note the pointed rock on the right, which I think is the turtle's head. From the same angle, another one:From the same angle, another one:From the same angle, a last one, more than a bit damaged, and pretty inconclusive:So the "graves" are found within the triangle, between these effigies (crows and turtles) at the corners. I have written about this before (here). The examples of white rock are not particularly spectacular.

Second Site:
If there were effigies here, I did not see them. I'll show some examples of piles with a white rock:
Many of the piles included bits of burnt rock as well as white rock. Spot the white rock, spot the burnt rock. Here is another:
Another:Closer:Another:Closer:Another:Closer:Burnt and white. See the pattern?

Some other noteworthy features at this site include a boulder with a chain of connected rocks, perhaps a "seat".And at least one pile incorporating a curious single rock that might have been specifically selected for.
Strange pits and holes in that one rock:Whether these sites are graveyards, I do not know. We have all heard there were Indian Graveyards. Thoreau wrote about their existence. But is there a description anywhere? Whatever the case, these types of sites have an identifiable character, with the white rocks and the burnt rocks and the curious rocks incorporated into the piles.

I want to mention explicitly that the piles at these sites are not evenly spaced and are not in lines. This is not a "marker pile" site although sometimes it seems that that is all there is out there.