Equinox Alignment Site

Since it is Fall equinox today, I am posting a site in northern RI that appears to have an equinox alignment.  Last year Larry Harrop told me that a tribal member had told him that there is a sacred site in these woods.  This is one possibility.
     Near the top of a hill is a 300 foot long wall.  There are no other walls nearby that may have been joined to it once.

 Close to the wall is a strange, flat topped boulder with three smooth grooves running along the boulder's long axis. There is a prominent one to the left in the top photo, and two shallower ones to the right.

The boulder seems to have some sort of gutter carved into the left side, and a stain visible on the right side at the end of the deeper groove.  The grooves feel smooth, as if they were ground into the stone.  The long axis of the boulder is aligned N-S.
Here is the area plotted in topo software:

The longer section of the wall has about a 285 degree bearing, suggesting Spring and Fall equinox sunsets. The grooved boulder is the yellow waypoint near the slight bend in the wall.
         I have read of grooved stones with gutters described as "sacrificial stones", especially one at America's Stonehenge in NH.  There's no evidence that these stones were used for Aztec-style  sacrifices.  It is  more likely that this boulder was used for some domestic purpose, such as food production, since the grooves are ground smooth.  It may have been easier to collect ground corn, acorns,  or even paint powder by pushing it along a groove instead of scooping it out of a round mortar.
      One thing that always impresses me when viewing plotted waypoints  of walls and boulders is the number of astronomical alignments. Some may be pure coincidence, some may be real observation points, and some may reflect a native desire to organize the landscape  in respect to the changes of the seasons.
     Maybe this wall and boulder were the sacred site, or maybe this other boulder is it:

This oblong boulder is propped at both ends, and has a "face" picked into the larger end. It is a long walk north from the alignment site. Or maybe the whole wood is sacred.
     In any case, the aligned wall and boulder were interesting subject matter for this painting. The best composition was facing away from the sunset.

Here it is spring equinox, and the shadows in the melting snow are parallel to the wall.