Let me write about the two sites outlined in red next to the yellow trail - locations are only approximate. The smaller site, a few feet from the trail junction, is visible from the trail. A first pile was just a small arrangement of rocks next to the beginning of a brook:A few feet downhill, also next to the brook, was a little table built against a rock:It is easy to imagine this as a small altar next to the brook.
At another spot where the yellow and blue trails are close together on the northeastern slope of the hill, one can see some large rock piles next to a brook there. I saw two of these just as it started raining hard. So the pictures did not come out well. Here was one - quite a big pile with big component rocks on a boulder, with a niche facing outward towards the brook.Another, from one side:From the other:This one seems to have a niche in it as well. So while we are on the subject of "altars" next to the brook, perhaps these have a similar intent. I saw three other of these large piles with large rocks, in the ferns, a few feet away up the brook. These were in the video here. Blurry photos here: and here:By this time I was soaked, so I did not get good closeups, or think to wonder if these also had niches. But on the way back out I saw another table like structure:During the walk I was thinking about the classification of most sites as mound-with-hollow sites, marker pile sites, or water-related sites. Here are what seem to be water-related piles and they might have a feature involving a table or a niche. Something to look for.
Finally, that small outline at the lower right is a marker pile site, looking out southwest over water, Hager Hill across the way: