The I-10 Projects: Layers of Prehistory in the Santa Cruz River Floodplain

1993 to present

Prior to improving interchanges and frontage roads along Interstate 10 (I-10) in and near the City of Tucson, the Arizona Department of Transportation (ADOT) entered into a Programmatic Agreement with the Advisory Council on Historic Preservation to achieve compliance with Section 106 of the National Historic Preservation Act. In 1993, Desert Archaeology developed a treatment plan (updated in 1998) for the known and expected archaeological resources in the construction right-of-way. Consultation with Native American tribes about the treatment and disposition of human skeletal remains expected during the work was facilitated by the Arizona State Museum. For each highway segment, archaeological survey, testing, and data recovery projects have preceded construction.

In each segment we excavated trenches specially designed to reveal the layers of the floodplain; these helped in understanding the contexts of buried archaeological sites and the characteristics of the Santa Cruz River and its floodplain during the prehistoric periods when the sites were occupied.

The Las Capas site (circa 1250-800 B.C.) contained several layers of deeply buried archaeological remains; therefore excavations were concentrated in only a few areas so the entire sequence of occupation could be efficiently revealed and sampled.

Among the discoveries at Las Capas were canals dating to before 1200 B.C., the oldest known north of central Mexico. One canal runs diagonally through the middle of this excavation area.

The Santa Cruz Bend site (circa 800 B.C.-A.D. 50) had significant subsurface archaeological remains that were extensive and shallow, so the overlying sediments were mechanically stripped away over a large area to expose the layout of an early village and its variety of buildings and other features.

One pit structure found at Santa Cruz Bend was much larger than the hundreds of others identified at the site and is thought to have been a ceremonial building used by the whole village.

Many of the hundreds of pit structures investigated at the Los Pozos site (circa 400 B.C.-A.D. 50) had burned, preserving many details of their construction.

The large, well-made ceramic vessels found at the Stone Pipe site (circa A.D. 50-500) are some of the earliest known pots in this region that were designed for everyday use.

An innovative approach to compliance was developed at the prehistoric Julian Wash site. Excavations focused on the direct impact zone for a major new highway interchange. Areas that would receive only potential indirect impacts were identified and specific preservation measures were developed in consultation with ADOT and the State Historic Preservation Office. These areas were set aside for preservation, thereby saving portions of the archaeological resource for the future, also saving the agency money and earning ADOT a preservation award from the state. Through grants that have been obtained from federal sources, these preserved areas will be developed into an archaeological park that will educate the public about this important archaeological site and the prehistory of the region.

Many significant archaeological discoveries were made during the I-10 archaeological work, which was primarily in the floodplain of the Santa Cruz River. The floodplain has been revealed to contain a rich record of prehistoric cultures.

• Work at several sites has pushed back, by thousands of years, the appearances of agriculture, pottery, canals, cemeteries, ceremonial buildings, and villages in southwestern North America.
• Exposures of large areas of later village sites have greatly increased our knowledge of the development of a local variant of the Hohokam culture in southern Arizona.
• The large quantities of new data obtained from these archaeological investigations have provided enough new information to revise many long-held ideas, as well as to develop new models about prehistoric cultures of this region and the Southwest in general.

The high visibility of our excavations beside the highway led to a high level of public interest and media coverage. Open houses and tours of the excavations were held for professional archaeologists, school groups, and the general public. Local newspapers and television news programs covered the archaeological work at each stage‹some of which was picked up by newspapers around the country and by National Public Radio. Articles about the many significant discoveries appeared in national scientific periodicals such as Science and American Archaeology.

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