I’m really not sure. That whole area up there was once Indian land and some of it still is home to many descendants, but the houses are all much further down the hill.
The fact that it spans three towns and two states makes me think it’s unlikely it’s anyone’s private property. Watch some YouTube videos and do some research on the area And perhaps you can enlighten me.
If you look up Stagg Hill Road in Mahwah New Jersey on the Google maps, you can see where the road ends up in the hills, about a mile from the route 17 exit. From there it’s nothing but woods and rocky trails for miles .