Hey, I have seen some of these way up in the northern parts of Pennsyvania too, one field has 7 of these circles. Its farm land with nothing on it right now. These are on a south facing slope. Sounds like I need to look closer at this, I am going to bear camp in a few weeks, that will put me right in the area.
There are many, many sites around the area Jeff, when I hunted we dug in the woods, but some of the farms I know of you cant see anything either. Some sites contain different time periods, some have many, you just gotta go look!!