On the grounds of Pima County's Ina Road wastewater treatment facility, archaeologists have unearthed the remains of an ancient farming community that could potentially rewrite the history of human settlement in the Southwest.
The less than auspicious setting might not inspire today — the scent of human waste at times overwhelming the senses — but scientists say the site was ideally suited for organized agriculture when the ancients farmed the area more than 3,000 years ago.
"This was the perfect place to start irrigation agriculture, and these guys did it in spades," James Vint said.
Vint heads up a team of more than 30 archaeologists and researchers with Desert Archaeology, Inc., working on the county-funded project called Las Capas.
The settlement dates from at least 1200 B.C., during an era of Southwestern history archaeologists call the Early Agriculture Period.
Positioned near the confluence of the Cañada del Oro, Rillito Creek and Santa Cruz River, research at the site has provided scientists with a glimpse into the transition from roaming bands of hunters and foragers to a society of skilled farmers — a snapshot of human progress in the Southwest.
Not surprisingly, the Santa Cruz has supported agriculture ever since. Even today, cotton farms line the river in Marana and Pinal County.
Las Capas flourished during what archaeologists call the San Pedro phase, a period dating roughly from 1200 to 800 B.C.
What most excited researchers working at the site was evidence that the people who once inhabited the area had created a system of canals. The early engineers found they could maximize their agricultural output by diverting the water flow from the Santa Cruz to adjacent fields.
"This is really the earliest evidence of such an extensive and well-designed irrigation system in the Southwest," Vint said.
Academics have long known of the Hohokam Indians' extensive canal systems that crisscrossed areas of modern Phoenix. That civilization thrived in the valley from about 1 to 1450 A.D.
Even though the Phoenix system eclipses the recent discovery in size, sophistication and scope, researchers marvel at Las Capas because it predates the Hohokam canals by more than 1,000 years.
"This has completely revised our understanding of when irrigation agriculture was introduced," Vint said.
The canals fed fields organized in asymmetrical grids. Workers could open and close earthen gates to regulate the flow as needed.
The excavations Vint and his team have done show the generations of maintenance work done on the canal system.
Archaeologists exposed a cross-section of one waterway that clearly shows sediment levels in the shallow canal. Color variations and lines like tree rings in the exposed soil gave scientists a window into the history of the system.
Vint said the canals likely held running water for as many as nine months out of the year.
Mounds piled along either side suggest people routinely cleaned sediment and other debris from the canals. The researchers also have found freshwater mollusks and snails in the sediment, further evidence of the abundant water that once coursed through the Tucson basin.
Based on the research done to date, Vint said the farming operation easily covered 100 acres and could have supported as many as 150 people.
When it came farming, in the second millennium B.C. — and today — corn was king.
"This wasn't Iowa corn," Vint said.
Maize, precursor to modern corn, first appeared in the Southwest more than 4,000 years ago. Societies in Central and South America have cultivated the plant for more than 6,000 years.
Ancient farmers along the banks of the Santa Cruz grew a variety similar to today's popcorn. Researchers surmise that dried kernels were popped and then ground into meal and used for tortilla-like cakes.
While the discovery of the canals revealed a methodical sophistication previously thought unknown in the Southwest, the people still relied on the natural abundance that surrounded them.
Las Capas residents likely foraged for much of their foodstuffs, gathering cactus fruit, mesquite pods and weeds like amaranth.
Human remains found at the site further enforce theories that the people had a varied diet.
"From the skeletal analysis done — these people were really quite healthy," Vint said.
The site also has revealed several circular pit houses and holes dug for cooking.
Reaching down to pile of rocks, Vint lifted a golf ball sized stone.
"This is 3,000-year-old charcoal," he said.
Because the people who lived here hadn't developed advanced pottery methods, most of the cooking was done in shallow pits. Fires were built, then piled with rocks filled with maize and covered with soil, rocks or grass. Scores of such cooking pits dot the site.
Evidence of human settlement in the area was first discovered in 1975, when a section of adjacent Interstate 10 was under construction. The highway today runs over an area that likely made up much of the village that the farming efforts at Las Capas fed.
Later, in 1998, archaeologists uncovered about two acres near the current site where thousands of artifacts and the remains of permanent settlements were discovered.
Workers in 1998 found a dog's skull at the site that appeared to have been deliberately severed from the body and buried. Analysis of the cranium revealed that the dog differed from wolves or coyotes, leading researchers to surmise that the animal weighed about 50 pounds.
The find also suggests that Las Capas residents domesticated dogs and possibly other animals during their long residency along the river bank.
Researchers have found evidence of at least seven other settlements dating to the same era. Those communities stretch from A Mountain south to Martinez Hill near Valencia Road and Interstate 19.
Like Las Capas, those settlements hug the Santa Cruz River, some showing evidence of canals.
After untold generations of harnessing the river's bounty, a catastrophic event forever changed life for the people of Las Capas. Progress, again, was on the move. A massive flood around 800 B.C. damaged the canals and cut short the residents' more than 500-year stay.
Vint said his team has unearthed evidence that people made attempts to rebuild the waterways, but ultimately abandoned the village. Where they went is unknown.
The evidence of how people lived at Las Capas remained covered in layers of sediment for thousands of years. Today, archaeologists race against the clock before another wave of human progress sweeps away all that remains of the ancient civilization.
Pima County Regional Wastewater Reclamation Department intends to build a much-needed expansion to the Ina Road treatment plant. The work here and expansion work planned at the Roger Road facility will enable continued growth and progress in the Tucson area.
The upgrades will double the facility's capacity and bring the county's effluent discharge up to state environmental standards.
"This is essentially a compliance project," said Loy Neff with Pima County's cultural resources office.
Because the development will expand into an area of known cultural significance, the county has to conduct research and recover archaeological artifacts.
"We enforce the same standards on ourselves that we do on private development," Neff said.
Desert Archaeology will work on the site through the summer, at which point Pima County will begin the treatment facility expansion.
"There can't be any growth in the county without this expansion," Neff said.
The county intends to have the expansion operational by 2015.
"It's only by the virtue of public-supported archaeology that this work is being done," Vint said.
Pima County will pay nearly $7 million for the excavation work at Las Capas. The county plans to donate all artifacts recovered to the Arizona State Museum, with the exception of human remains, for which the Tohono O'odham Nation has claimed repatriation rights.