In the Andean foothills of Peru, not far from the Pacific coast, archaeologists have found what they say is evidence for the earliest known irrigated agriculture in the Americas.
An analysis of four derelict canals, filled with silt and buried deep under sediments, showed that they were used to water cultivated fields 5,400 years ago, in one case possibly as early as 6,700 years ago, archaeologists reported in a recent issue of The Proceedings of the National Academy of Sciences.
Other scholars hailed the discovery as adding a new dimension to understanding the origins of civilization in the Andes.
The canals are seen as the long-sought proof that irrigation technology was critical to the development of the earliest Peruvian civilization, one of the few major cultures in the ancient world to rise independent of outside influence.
It was assumed that by 4,000 years ago, perhaps 1,000 years earlier, large-scale irrigation farming was well under way in Peru, as suggested by the indirect evidence of urban ruins of increasing size and architectural distinction. Their growth presumably depended on irrigation in the arid valleys and hills descending to coastal Peru. But the telling evidence of the canals had been missing.
Then Tom D. Dillehay, an archaeologist at Vanderbilt University, started nosing around the Zaņa Valley, about 40 miles from the ocean and more than 300 miles north of Lima.
On the south side of the Nanchoc River, he and his team uncovered traces of the four canals, narrow and shallow, lined with stones and pebbles, extending from less than a mile to more than two miles in length. The canals ran near remains of houses, buried agricultural furrows, stone hoes and charred plants, including cotton, wild plums, beans and squash.
"The Zaņa Valley canals are the earliest known in South America," Dr. Dillehay's team wrote in the journal article. He added, by e-mail from Chile, that they were the "earliest in the Americas."
The initial discovery was made in 1989, but it took years of further excavations, radiocarbon dating and other analysis before Dr. Dillehay felt ready to announce the find.
"We wanted to make sure that the dates were correct and to find more early canals," Dr. Dillehay said. "There are now four sites with canals and probably more."
The authors of the journal article - Dr. Dillehay, Herbert Eling of the National Institute of Anthropology and History in Mexico and Jack Rossen of Ithaca College - said the system appeared to be a small-scale example of organized irrigation technology that "accompanied a mixed economy of incipient agriculturalists, plant collectors and hunters."
They reported finding no evidence of a centralized bureaucracy to manage the canals or mechanical devices to control flow rates. But the people of the valley understood elementary hydrology. They laid out the canals to use gravity to deliver river water down gentle slopes to the cultivated fields.
Craig Morris, a specialist in Peru archaeology at the American Museum of Natural History, who did not take part in the research, said, "Their use of slope and management of water flow shows again that ancient people were a lot smarter and more observant than we often give them credit for."
Jonathan Haas, an archaeologist at the Field Museum in Chicago who has excavated urban sites elsewhere in Peru's coastal valleys, called the canal discovery "a difficult and brilliant piece of work."
In their own excavations, Dr. Haas and Winifred Creamer of Northern Illinois University have uncovered remains of urban centers of a complex agricultural society that flourished 5,000 years ago in valleys in a region known as Norte Chico, or Little North.
Such an arid region would have had to have irrigation to have agriculture, especially on an apparently large and prosperous scale.
Dr. Haas said the new discovery appeared to show the early irrigation technology that the people of Norte Chico then adopted and expanded to "bring about a cultural transformation" 400 years later.