Invisible Mounds - invisible but necessary

There is something poignant about the mound there, a bit to the left in back, almost invisible. Houses a few feet beyond.

I gotta say this location is very very typical. So much so, that the placement at the tops of ravines (this is above Wolf Brook, Townsend) cannot have been optional.
Maybe this is a good time to post a similar location from Carlisle: this is visible to the west from Lowell Rd, on the way to Concord. This is also at the top of a ravine, in a similar disposition but looking much fresher: 

 

So, what I am saying is that no gully goes un used. Compare locations: in Townsend vs in Carlisle:

 It suggests a required behavior.