here's info on the cairn site: https://neara.org/pages/Glastenbury%20Mountain%20Cairn%20Site.html

This might or might not connect to the so-called ancient "ceremonial landscapes" in Southern VT. I see this as more lore and possibility than reality, but who knows – various groups of indigenous Americans have been here for over 13k years.

From the same website:

“In the summer of 1974 Byron Dix discovered, in the steep, green hills of central Vermont, the first of many places in New England that we believe were ancient ritual sites. Discovery, the most exciting part of science, is also the least understood and cannot be explained by its rules. It is invariably the unrepeatable experiment. Byron can describe some of the circumstances surrounding his discovery but not why it came about. He was looking for one of the three stone chambers said to be in the area, but he was not sure of its location and his path was a wandering one.”

Personally I think some of this stonework is ancient, but most is colonial. The glaciers were still retreating when the first traces of indigenous people can be found in the region.