http://www.ancient-origins.net/news-history-archaeology/fire-not-corn-was-key-prehistoric-survival-arid-southwest-usa-009203/page/0/1
Fire, not corn was key to prehistoric survival in the arid Southwest USA
Sullivan has pieced together clues firsthand and from scientific analysis to make a persuasive argument that people used fire to promote the growth of edible leaves, seeds and nuts of plants such as amaranth and chenopodium, wild relatives of quinoa. These plants are called "ruderals," which are the first to grow in a forest disturbed by fire or clear-cutting.
Fanning the Flames of the Theory
Sullivan also studied the geologic layers at these sites. Like a time capsule, the stratigraphic analysis captured the periods before and after people lived there. He found higher concentrations of wild edible plants in the period when people lived there. And when people abandoned the sites, the area they left behind saw fewer of these plants.