He has spent two decades leading field research in the Grand Canyon National Park and the upper basin in the region. His evidence shows the ancient people of the area used fire to promote the growth of edible leaves, seeds, and nuts like amaranth, goosefoot, and chenopodium, wild relatives of quinoa, and calorie rich nuts and berries. Researching thousands of clay pots, he and his students have found 6000-7000 pollen grains and only six were corn. He also found that there was more evidence of wild edible plants then when people left these sites. He also looked at the area after a massive wild fire in 2016, and edible plants were growing there a month later in abundance.

This is not to say that other people in the Ancient Southwest were not more dependent on corn. There is more evidence for it outside of the area in question.

(My note: It seems to me that the same techniques used in this study should be applied elsewhere in the Southwest to test whether corn dependency is as prevalent as we have thought).

Eurekalert has the report here:
https://www.eurekalert.org/pub_releases/2017-11/uoc-asf112717.php