Long stone mounds and small "snake effigy" high up in the Trapfall Brook Watershed

With reference to the map here.
I was walking down a gully, before it joined the main brook, and saw a collection of rocks that seemed too clustered to be random:
There is a white feldspar rock in the near-ground, then three rocks, then a regular curve of cobbles, ending in a small ring of stones:

 The white feldspar

 You can see this is a well-formed structure:

 The terminal ring of stone

We have seen several examples of curvy "snakes" like this, ending in a similar small circle. [Try Googling "the body of a snake, with the circle as the snake's head". See also for example here.]

Previously (see first link above), I described some of the other things in those woods. As I walked back up hill to the east, I came across a long mound. Here it is at the foot of the slope, with wetland to the left and behind me:

 

Let's have a look at the mound's surface, starting from the end on the right:

In the foreground there is a faint depression on the left, and a piece of beige quartz on the right:

 Part way along the mound was another faint depression:

And nearby, but not exactly adjacent, a small chunk of quartz:

At the other end, a small depression - or bite - with white feldspar at either end of the bite.

We are north of the Fitchburg Reservoir here. Such longer mounds and berms seem more typical up here than the rectangular mounds I see south of the Fitchburg Reservoir. It is very tempting to compare this structure to the mound on Blood Hill, a mile or so to the south (see here.) 
It is also tempting to compare with a further mound I spotted very briefly while driving up Whitemore Hill Rd on the main hill. I parked hastily - not sure if I was trespassing - and grabbed pictures:

Just a glimpse, but this looks like another long mound:

There are plenty more woods where these came from and there seems to be plenty of ceremonial stonework there. So I'll have to go back and do some more exploring.
UPDATE: see later comments here http://rockpiles.blogspot.com/2013/11/whittemore-hill-new-ipswich-nh.html