This may be a different site, but CNN
showed a very brief overhead shot of a site
near Miami with presumably
prehistoric stonework.  It was no
Stonehenge, however.  The stones were
not stela but rather low and adjacent, such
as a foundation or pavement.  The
announcer mumbled something about
"scientists think it may have been used to
determine seasons," so there may be a
slight similarity as an observatory.  The
footage on CNN showed a very interesting
site, though.