Top 10 Discoveries of 2009 - Early Irrigators - Tucson, Arizona

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(Courtesy Desert Archaeology Inc.)

For years, archaeologists in the American Southwest have wrestled with a frustrating puzzle: How did ancient farmers grow corn in the cactus-studded Sonoran Desert as early as 2000 B.C.? Some form of irrigation was clearly necessary, but until 2009 no one had ever seen evidence for one of these primeval watering systems. Now at the site of Las Capas outside Tucson, archaeologist James Vint of Desert Archaeology Inc. and his colleagues have excavated an enormous network of canals and fields stretching over as many as 100 acres and dating to 1200 B.C. It is the oldest documented irrigation system in North America.

After exposing the site with three backhoes, Vint's team traced the ancient flow of water from the nearby Santa Cruz River to a series of at least eight canals and a regular pattern of fields, each measuring about 250 square feet. Vint marvels at the latticelike design of the Las Capas waterworks. "The site is located in an ideal place for canal irrigation," says Vint, "and in terms of moving the water, the builders had it figured out really well."

Preserved down to the finest details--including planting holes--the ancient agricultural system is now raising the question of just who the people were that constructed it. Researchers had long envisioned the region's inhabitants at this time as mobile hunter-gatherers for whom agriculture was largely a sideline. But the discovery at Las Capas, says University of Arizona archaeologist Suzanne Fish, "is making everyone rethink who these people were. There's just so much intensive labor there that it's hard to see the builders going off and leaving it."

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