Work in the Southwest United States and Northwest Mexico (also called the Southwest/Northwest) over the past 25 years has revolutionized our understanding of the diffusion of domesticated plant species into North America from the Balsas River Basin of southwestern Mexico, as well as our knowledge of the transition from hunting and foraging to settled agricultural lifeways. Much of this knowledge has come from work conducted as part of cultural resource management projects, a type of work that is required and funded by Federal, State, and local government agencies in advance of development projects.
The Tucson Basin, and the modern city of Tucson, Arizona, are situated along the Santa Cruz River in the Basin and Range environment that extends from central Arizona to north Mexico. Located in the sub-tropical Sonoran Desert, this is one of the most diverse biomes on the continent, with a mosaic of economic opportunities afforded by the elevation changes from rich riparian zones 2000 ft (600 meters) above sea level to alpine mountain ranges 10,000 feet (3000 meters) high.
The period we discuss here is called the Early Agricultural period, which spans the two millennia from about 4100 to 1950 years ago. It begins with the first introduction of maize – perhaps the most widely known and famous Mesoamerican cultigen –(e,as a minor tended crop plant, and ends with the development of an agricultural lifeway with significant dietary, social, and ritual dependence on maize.
Las Capas Aerial,Ag Field Close-up,2009
Prior to the 1990s, much of what was known about this period was based on limited information from charcoal and burned features exposed in arroyo cuts or other deeply buried contexts. Because of a series of deep excavations in advance of highway construction, the expansion of a major wastewater facility, and related infrastructure improvement projects in the Tucson Basin, today more than 25 archaeological sites with early maize have been discovered along the Santa Cruz floodplain, making this region the best studied Early Agricultural period landscape in the Southwest/ Northwest. Whereas archaeologists had focused primarily on the “when” and “where” of early maize found in various discovery contexts between Mesoamerica and North America, this new work exposes the settlements and working landscapes of the people who adopted maize, allowing a far more anthropological understanding of the period, and how people took up agriculture and incorporated it as a part of daily life.
Our company, Desert Archaeology, has been privileged to conduct much of this work. We, and other archaeologists, have found early corn along the Santa Cruz River that dates as early as 5700 years ago. Maize had spread to a wider range of environments by around 4500 years ago. The earliest cultivation was doubtless simple flood-plain farming, which, although not strictly an intensive endeavor, did require knowledge of how, when, and where to plant seed, and how to bring the plants from seedling to maturity, and to carry over seed for the next growing season. It is interesting to note that the earliest canal documented in the Tucson basin dates to 3500 years ago, contemporaneous with the earliest known canal features found in central Mexico. This raises the question: Was irrigation developed independently in Mesoamerica and the Southwest/Northwest, or was that technology brought rapidly from Mesoamerica northward via diffusion or migration of farmers? The ongoing work here will help to address this issue.
Las Capas aerial overview, 2008.
Las Capas, which means “the layers” in Spanish, is one of the largest and most extensively documented Early Agricultural period sites in the Southwest/Northwest, and also one of the best preserved. It is located at the confluence of three rivers, the largest of which is the Santa Cruz, and the remains from this time period are buried below 1 to 3 meters of sediment, invisible on the modern ground surface. Several limited investigations had been conducted at the site over the past 30 years, but in 2008 and 2009 while working for Pima County, the local municipality, Desert Archaeology conducted extensive investigations in advance of the expansion and improvements to the Tres Rios Water Reclamation Facility. Over 60 acres of the site remained intact, allowing documentation of not just an archaeological site, but a substantial piece of the prehistoric agricultural landscape.
Over 13 months of fieldwork, more than 5500 prehistoric features from approximately five centuries of occupation between 3200 and 2700 years ago were documented on the ancient floodplain. More than 60 percent of these were excavated, including 53 pithouses, 8 possible pithouses, 2758 storage pits, 490 roasting pits, 20 inhumations, 2 cremations, and 11 animal burials, among other features. Over 113,000 artifacts and 7,300 samples were collected. The most impressive feature at the sites was a 15 hectare system of irrigated fields built, used, maintained, destroyed by floods, and rebuilt, for over 400 years. Main canals in this system averaged 1.5 meters wide and 0.75 meters in depth, with secondary and tertiary canals branching off to irrigate 4-meter by 6-meter field cells.
Previous fieldwork at the site showed long term residential use of the alluvial fan at the margin of the floodplain, and although the full extent of the occupation remains unknown, we can see the patterns in the use of the landscape. The houses were small, circular to oval brush structures capped with dirt or mud. Houses, and their extramural storage pits, were built in small clusters of 3 to 8 structures, situated on low rises toward the floodplain margin. Roasting pits were built on the peripheries of these house groups, and the fields were located some 20 or more meters away on the river floodplain, toward the river channel. The overall village population was low, with perhaps no more than 75 to 100 people living in the settlement at a given time, and only 500 or 600 people in five or six contemporaneous communities along the Santa Cruz River floodplain overall.
Significance of research
The vast exposures documented both within the site of Las Capas, and along the Santa Cruz floodplain through the Tucson Basin, have transformed our understanding of the transition from foraging to farming in the Southwest/Northwest, but the work has global applications for understanding the natural and social ecology of this transition, the processes of diffusion of food and knowledge, and for understanding the Neolithic Demographic Transition in the North American Southwest.
In contrast to the Neolithic Demographic Transition in Europe and West Asia, in which the adoption of domesticates and population growth were clearly correlated and gave rise to a substantial rapid increase in population and village life, the consequences of adopting agriculture were less sweeping in scope in the Southwest/Northwest. Maize was incorporated at low levels into the local economies for the first several centuries after its diffusion northward from central America. Its importance in the diet grew slowly but inexorably, and the immediate demographic effects of the domesticate as a new food source appear to have been few. Furthermore, environmental, social, and demographic diversity resulted in maize agriculture being adopted at differential rates in the greater Southwest/Northwest. Significant population growth did not occur until the development of ceramic vessels some 2,000 years after introduction of maize to the region, which allowed for more efficient cooking and long-term storage of the plant’s grain.
As such, the extensive nature of the canal systems and the necessary investment in construction and maintenance documented at Las Capas present something of a paradox. The maize cobs were small, no more than 10 cm long and with 10-14 rows of kernels; grain yield was low. Maize provided only a portion of the diet of the people who lived at Las Capas. No more than a third of caloric intake, probably less, was devoted to maize in a diet otherwise dominated by use of rabbits and deer, mesquite pods, foraged leafy greens and seeds from grasses and sedges that grew on the floodplain or were tended in the margins and disturbed soils of the fields. The dietary importance of maize as a food may have been relatively minimal during the first several centuries of the Early Agricultural Period. Where its greatest significance lay was perhaps in the social dimensions of agriculture as the practice became ever more integral to community identity and existence: the need for organized labor to plant and harvest; the cooperation in building and maintaining field systems; scheduling and conducting irrigation cycles and managing water resources; the ritual practices to ensure successful crops; the production and storage of seed corn and surplus to perpetuate the cycle for another year; the gathering of people and communities at planting and harvest to feast and share news; the farmer’s participation in the cycle of renewal and looking to the future that is the essence of being part of the land. These changes were developed around maize, as it alone of the “three sisters” entered the Southwest/Northwest early. Squash and beans—the other two core Mesoamerican domesticates– are not found in the Southwest/Northwest until around 3100 and 2800 years ago, respectively.
The Early Agricultural period is also a period of early transformation of social networks. Not only are there the Mesoamerican connections of maize and ritual, but pragmatic regional networks link the site to its neighbors. Probably no more than six farming communities the size of Las Capas could have been supported by the Santa Cruz River; water was the limiting factor. Communities that relied on the river for irrigation by necessity had to negotiate when and how much water could be drawn onto their fields. Social and political capital was required to organize the allocation of not just water, but access to farmland as communities became anchored to place and population began to grow. Low-level itinerant gardening developed into labor-intensive and sociallyintensive agriculture that was centered on maize as both food and identity. And interaction was not simply among communities within the Santa Cruz River valley. Styles of projectile points indicate links with early farming communities several hundred kilometers to the south, in the Rio Boquillas region of Sonora, Mexico. Jewelry made from marine shells that originate on the California coast demonstrates trade relations among groups over long distances. Similarly, stone tool artifacts made of obsidian from multiple distant volcanic sources have been recovered. People were connected over distances and social networks much greater than might be assumed at this early time.
Preservation Significance: Funding for Archaeology in the United States
Today, most of the archaeology conducted within the United States is funded as part of pre-construction environmental studies. At the national level, the National Historic Preservation Act of 1966 will soon have been in place for 50 years. Since that law was passed, other laws and regulations have been developed at state and regional levels. New insights into the earliest agriculture in the southern Southwest has been funded by contracts tied to all of these administrative levels -- federal, state, and local. The Las Capas project is highlighted here because it was the largest and produced the most dramatic results. The funding provided by Pima County, the project sponsor, was at a scale that matched the extensive nature of the Tres Rios Water Reclamation Facility. The coming together of a large project, adequate funding, refined field methods by experienced field personnel, and an adequate time frame to do high quality work at this remarkable archaeological site were the essential conditions that led to ultimate success.
Desert Archaeology, Inc.
Desert Archaeology, Inc. was founded in 1989 and is based in Tucson, Arizona with a branch office in Phoenix, Arizona. The firm has 35 employees and works primarily within the state of Arizona. Since its founding, Desert Archaeology staff members have completed over 2,200 projects, from brief surface surveys to major excavations. Funding comes from contracts for compliance with cultural resource laws. In 2009, Archaeology Magazine named Desert Archaeology’s project documenting early irrigators from 3,000 years ago in Tucson as one of the Top Ten Discoveries of the Year. Desert Archaeology completed a series of large-scale projects along the Santa Cruz River of the Tucson Basin since the 1990s that have transformed our understanding of the arrival of agriculture in the American Southwest.
William H. Doelle
William H. Doelle received his Ph.D. from the University of Arizona in 1980. He is currently founder and President of Desert Archaeology, Inc. and President and CEO of the nonprofit Archaeology Southwest. His research interests are the large-scale demographic and cultural changes of the American Southwest and Mexican Northwest from A.D. 1200 to 1700.
James M. Vint
James M. Vint received his B.A. in Anthropology from the University of Arizona in 1987 and his M.A. in Anthropology from Northern Arizona University in 1992. He has studied and practiced archaeology in Arizona and northern New Mexico since 1983, and has worked for the Arizona State Museum, National Park Service, and, since 1993, for Desert Archaeology, Inc. His research interests include community development and identity during the Early Agricultural period and Protohistoric period – the bookends of the agricultural demographic transition in the Greater Southwest/ Northwest.
Sarah Herr is a Research Archaeologist at Desert Archaeology. She received her A.B. in Anthropology and Classical and Near Eastern Archaeology from Bryn Mawr College in 1991 and her M.A. (1994) and PhD (1999) from the University of Arizona, Department of Anthropology. Her research interests include demographic studies of frontiers, the transition to village life in the Southwest United States, the early history of the Western Apache, and the history of archaeological practice and cultural resource management in North America.
(William Doelle James Vint Sarah Herr Desert Archaeology, Inc.)
(Source: Research Center for World Archaeology, Shanghai Academy)