The discovery of a prehistoric irrigation system in the Marana desert (Arizona, USA) is giving archaeologists a deeper glimpse into one of the first groups of people to farm in the Tucson basin. "What we're looking at is, perhaps, the earliest sedentary village life in the Southwest with people depending on agriculture as a primary food source," said project director Jim Vint.
     For more than 3,000 years, an elaborate ancient irrigation system has remained hidden deep beneath the sand in Marana. In January, excavation at the Pima County Regional Wastewater Reclamation Facility revealed the ancient irrigation system. It is said to be the most intricate system of its kind uncovered in North America. "We've uncovered dozens of these fields. We can see the actual holes where they planted the corn in many instances" geologist Fred Nials said. "We can completely reconstruct their irrigation system."
     The excavation, by Desert Archaeology Inc., complies with state and county regulations requiring that a site be excavated before development of land that may contain historical artifacts. What the archaeologists found was more than they ever expected, said Desert Archaeology President Bill Doelle. "Usually what people have found when digging in the flood plain is the main irrigation ditch that diverts water out of the river; they'll just see that ditch," he said. "We had no idea that whole field systems are also preserved in that flood plain sediment."
     The field system spans about 60 to 80 acres and was revealed by scraping away thin layers in broad 7-foot sections using a backhoe. The archaeologists have now discovered more than 200 individual maize fields and more than 170 canals of various sizes throughout six major layers of sediment. The topmost or most recent layer dates to 800 BCE, and the sixth layer, which is about 13 feet underground, dates to about 1200 BCE. These 'layers,' produced by periodic flooding of the river, reveal the story of one of the first groups of people to recognize the enormous potential of the Santa Cruz River and agriculture. These pre-Hohokam peoples, thought to be ancestors of today's Tohono O'odham Indians, depended on the river for their livelihood.
     "We pay attention to the river intermittently when there is a major flood event or something, but otherwise we don't pay all that much attention to it anymore," Doelle said. "It was the lifeline for this area throughout all of prehistoric times." The lack of crop variety in the fields suggests that this was one of the earliest attempts to shift away from a hunting and gathering lifestyle, said Vint, Las Capas project director. Archaeologists at the site have also found a variety of hunting tools, as well as human and animal remains. The recovered artifacts will be analyzed and logged, then sent with photos and maps to the Arizona State Museum to be curated.

Source: Azstarnet.com (27 September 2009)