The grassy knolls around the site suggest that the locals hunted and farmed in olden times.
#1, I think Fedora is on to something. ;')
#2, I'd be surprised if those "knolls" don't turn out to be more ruined structures. It's almost entirely unheard of to find some kind of large communal structure (whether it was a temple, or a palace, or a fortress, or a market of some kind, or something else, or some combo) and not find it surrounded by a settlement of some size.