The Discovery of Las Capas Agricultural Irrigation Canal System

In 2009 the oldest agricultural irrigation canal system ever found in the United States was discovered in Marana and it rewrote history.

Named “Las Capas,” for the layers of soil and mud from the Santa Cruz River that leave distinctive striations (and stratigraphy) that reveal thousands of years of canals in the same place, this archaeology site is a 4,000 year-old irrigation canal system that covered more than 100 acres west of the I-10 freeway at Ina Road.

The irrigation canal system was constructed for large scale cultivation of maize (corn). Its discovery pushed back the dates previously established for large scale agriculture in the U.S. by a thousand years.

Because of the discovery of the Las Capas site it is now known that there was sophisticated farming here during the Late Archaic-Early Agricultural (1,200 B.C.E. - back) period, and it is speculated that evidence of even older large scale farming at this same location will be discovered. This is one of the reasons why this area received the Santa Cruz Valley National Heritage Area designation in 2018.

Continuing discoveries in Marana paint a picture of a populated area along the Santa Cruz River that was nearly continuously occupied from 13,000 years B.C.E. to present, and part of a vast cultural network that stretched to South America and across the United States. The Late Archaic cultures up to the Hohokam cultures (1200 B.C.E. - 1,200 A.D.) here were based around farming many types of crops. About 1,000 years ago, the Hohokam (who also farmed maize) farmed agave using specialized rock constructs to grow agave murpheyi for food, fiber, and possibly trade. This type of agave doesn't naturally grow in the desert floor region on poor rocky bajada soil. Clever farming strategies allowed for the cultivation of as many as 42,000 agave plants at one 1,200 acre farm site in the Marana area.

But the main story is about corn agriculture. Corn was first domesticated 9,000 years ago from a wild grass variety called teosinte in the Balsas River Valley near Mexico City. Teosinte only yields about nine kernals per ear, however, and is no where near the size of ancient or modern corn. It is currently believed that about 5,000 years ago, domesticated teosinte, that had previously reached South America, was further cross-bred and developed by farmers in western Bolivia and Brazil, into a much larger type of corn that was viable as a food staple. This new improved corn spread back from South America through Mexico and reached (what we now call) Marana, Arizona at least 4,000 years ago.

That is what we know as of today. Ongoing archaeology in Marana turns up new discoveries all of the time and continues to add to the story of early agriculture in the Americas. We will update the story as it unfolds.

Discover the Santa Cruz Valley National Heritage Area here.

Further reading about the history of Hohokam and pre-Hohokam in this area here.

Main photo image is a reconstruction of Las Capas by Rob Ciacciore for Desert Archaeology, Inc. Aerial image courtesy Desert Archaeology, Inc.

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