Residue was found in the old dump sites (as in “taking a”) in the dried up feces which showed humans had been on the menu, among the Anasazi. The archaeology had already shown that the society had gone through major stress with wall divisions inside the residences and such. And it isn’t limited to the Anasazi, by any means, not even counting the devouring of human hearts cut out vivisection-style by the Aztecs.
http://www.google.com/search?q=sw+precolumbian+cannibalism
From what I understand the Toltecs were the worst brutal offenders.