A "village" of small rectangular piles with hollows

In this area of northeastern Groton there seem to be rock pile sites of different ages including a strong component of the tradition of rock piles with hollows. Looking at the map there is an obvious adjacent area to be explored.

Last weekend, I went back to take a look at what appeared to be crescent shaped piles that I found just after snow started to accumulate (see here). I missed them at first but instead found maybe ten or more piles like this:From another angle:You can see it is a small rectangle with an empty hollow area in the center. Here is different one:
Other piles appeared like ridges:I guess this is the same thing but damaged differently. Was this a crescent?

Another variation was piles with fewer, larger rocks, and larger mounds:Here is another small one with a hollow, the same larger mound in the background.As you can see from the topo map, this site is in a valley. The site is along the edge of a wet area.
Let's take a closer look at the large mound. Its level surface is particularly incompatible with a practical rock dumping explanation for the pile. This pile sits at a sort of nexus of the stone walls there. Also, in the vicinity, a pretty nice "cairn"a pretty nice flat-faced pile on a boulder:a pretty nice gap pile:Still other small rectangular piles, badly beaten down, with a hint of a hollow.Compare to this next:I think the remnants of structure are still visible but these must be of a different age from the still fresh "pretty nice" piles above.

As I walked back out, I finally came back to the crescents I photo'd in January. Now I think they were just snow covered examples of these small rectangular piles with hollows. The main "spine" of the pile somehow persists, giving them a curved, tailed, or slight crescent shape.

Update: The apparent difference in ages of piles with hollows versus the "pretty nice" piles is an example of rock pile half-life: the idea that older piles will be more damaged. That leads to the possibility of a chronology, if not a calibrated age for different styles of rock pile. In this case it simply restates the obvious, that the ones with hollows are older. But the existence of this site, with the combination, allows for comparison of the styles.