CHACO CANYON SOILS WERE NOT TOO SALTY TO GROW CROPS SUCH AS MAIZE BEANS AND SQUASH FOR MORE THAN 1200 PEOPLE WHO LIVED THERE

Researchers have long debated whether the people who lived here between 800 and 1300 AD were self-sufficient or relied partially or entirely on imported food to survive. These ancestral Puebloans built elaborate adobe structures, some of them four stories tall and recessed among cliff faces under the hot New Mexico sun. UC's soil analysis suggests that the most significant challenge for growing crops was irrigation. That's where ancestral Puebloans demonstrated particularly adroit farming skills and perceptive land management, said Jon-Paul McCool, a UC graduate and lead author of the study.

"The major limitation is water. You couldn't rely on rain for field agriculture," McCool said. "You'd have to gather and control water, which we know people in the region did." McCool earned PhD and master's degrees in geography and museum studies at UC and now teaches at Valparaiso University.

The study was published in June in the journal PLOS ONE.

Dunning said the study was able to determine that the soils could support agriculture in Chaco Canyon and that irrigation canals found at the site were built at least as early as the eighth century. "The evidence is compelling that they produced most of the food that they consumed in Chaco Canyon and devised sophisticated irrigation strategies to do it," Dunning said.

Today, Chaco Canyon sees about 9 inches of rain per year, four times less than the breadbasket of the American Midwest. To make the most of this precious resource, ancestral Puebloans built elaborate canals to divert rainfall to their farm fields. UC researchers re-examined soil samples taken from sites in and around Chaco Canyon. While some of these sites indeed did have saline levels too high to support agriculture, that was the exception, researchers found. Instead, researchers found that the desert soils were not much different from soils in other parts of the Southwest where agriculture was practiced. "The evidence is persuasive that they grew their own food," Dunning said.

UC's team consisted of geologists, archaeologists and biologists. They spent weeks each summer studying different aspects of Chaco Canyon. Many of the study sites are accessible only by foot so researchers would hike in at dawn before the afternoon heat became too oppressive. A collapsible tent shelter provided some relief from the sun.

UC's research is adding to what scientists already know about ancestral Puebloans in New Mexico. These former occupants of Chaco Canyon left behind evidence of having traded goods with people from distant places. Archaeologists have found seashells from California and macaw feathers and cacao from Mexico.

The people of Chaco Canyon left behind petroglyphs carved into the rock -- drawings of animals, people and symbols. These included the famed "Sun Dagger," a notch in a slot canyon that casts a dagger-shaped beam of light onto a shaded rock face upon which is a carved petroglyph spiral that marks the sun dagger's path across the wall over the four seasons. They also were known for their turquoise carvings, including a famous frog figure among the collection of the National Park Service.

Scientists still aren't sure why the population of Chaco Canyon declined over the centuries. Chaco Canyon continued to be occupied intermittently after 1300.