Ancient corncobs unlock riddle By MIKE TONER The Atlanta Journal-Constitution Prehistoric populations in the American Southwest transported corn over long distances -- and used networks of "farm to market" roads that enabled them to support large cities in areas that were unsuitable for agriculture. New studies of ancient corncobs show that large urban complexes like Chaco Canyon that thrived a thousand years ago in New Mexico imported corn from fertile farmlands that were 50 miles or more from major population centers. Archaeologists have long wondered how the sophisticated Chaco civilization, which built huge multistory dwellings in the high desert of...