Most of it, whats left, is dry layed stone. There are several trenches with an "Altar" with what looks like blood grooves. But the site is confused, what ever it is it ain't Injun. If you look at a map of the Merrimack River from Newburyport to Lawrence the site lies at the intersection of Methuen, Haverhill, and Salem, NH. The river has been dammed and the course changed in that area. Main drainage area for central NH.
One of the problems is that there has never been a real Archaeological survey of the area, mainly because of the Noble Redman problem and the people that own the site.
It is an interesting place to go and it is different, but until some people loose their attitude it is GGG speculation.