Publications
Cultural resource databases represent the single largest compilations of archaeological site data, but these databases are seldom used in research because they were designed for management purposes, evolved from paper-based inventories, contain significant interobserver variation, and record information inconsistently. In this paper we present methods designed to alleviate these problems in an analysis of more than 3,000 ancestral Pueblo habitation sites from southwestern Colorado. Our methods draw heavily upon Bayesian statistical concepts and utilize the rich excavation records of our study area to quantify the relationship between surface evidence and excavation results using probabilities. This approach offers a number of advantages over ad hoc, judgmental approaches, and produces a more empirically justified history of ancestral Pueblo settlement in our study area. We believe methods like these have great potential for reconstructing settlement patterns from survey data.
We propose that the development of leadership structures in northern Pueblo I societies can be understood as the most available solution to the assurance game (or trust dilemma) that these rapidly growing societies were faced with as they attempted to maintain traditional high levels of deer harvest in increasingly depleted landscapes. Results from agent-based models, and large faunal assemblages from the Dolores Archaeological Project, provide frameworks that underpin our assumptions and conclusions.
Maize is the New World’s preeminent grain crop and it provided the economic basis for human culture in many regions within the Americas. To flourish, maize needs water, sunlight (heat), and nutrients (e.g., nitrogen). In this paper, climate and soil chemistry data are used to evaluate the potential for dryland (rain-on-field) agriculture in the semiarid southeastern Colorado Plateau and Rio Grande regions. Processes that impact maize agriculture such as nitrogen mineralization, infiltration of precipitation, bare soil evaporation, and transpiration are discussed and evaluated. Most of the study area, excepting high-elevation regions, receives sufficient solar radiation to grow maize. The salinities of subsurface soils in the central San Juan Basin are very high and their nitrogen concentrations are very low. In addition, soils of the central San Juan Basin are characterized by pH values that exceed 8.0, which limit the availability of both nitrogen and phosphorous. In general, the San Juan Basin, including Chaco Canyon, is the least promising part of the study area in terms of dryland farming. Calculations of field life, using values of organic nitrogen for the upper 50 cm of soil in the study area, indicate that most of the study area could not support a 10-bushel/acre crop of maize. The concepts, methods, and calculations used to quantify maize productivity in this study are applicable to maize cultivation in other environmental settings across the Americas.
Chemical and nutrient analyses of 471 soil samples from 161 sites within four archaeological regions (Pajarito Plateau/Bandelier, Zuni, Mesa Verde, and the Chaco Halo) were combined with historical climate data in order to evaluate the agricultural productivity of each region. In addition, maize productivity and field-life calculations were performed using organic-nitrogen (N) values from the upper 50 cm of soil in each region and a range (1–3%/year) of N-mineralization rates. The end-member values of this range were assumed representative of dry and wet climate states. With respect to precipitation and heat, the Pajarito Plateau area has excellent agricultural potential; the agricultural potentials of the Zuni and Mesa Verde regions are good; and the agricultural potential of the Chaco Halo is poor. Calculations of N mineralization and field life indicate that Morfield Valley in Mesa Verde should be able to provide 10 bu/ac of maize for decades (without the addition of N) when organic N-mineralization rates exceed 2%. Productivity and field-life potential decrease in the following order: Zuni, Mesa Verde, Bandelier, Chaco Halo. The Chaco Halo is very unproductive; e.g., 10 bushels per acre can be achieved within the Halo only from soils having the highest organic N concentration (third quartile) and which undergo the highest rate (3%) of N mineralization.
Using the occupation histories of 3,176 habitation sites, new estimates of maize-agriculture productivity, and an analysis of over 1,700 construction timbers, we examine the historical ecology of Pueblo peoples during their seven-century occupation (A.D. 600–1300) of a densely settled portion of the Mesa Verde archaeological region. We identify two cycles of population growth and decline,the earlier and smaller peaking in the late-A.D. 800s, the later and larger in the mid-A.D. 1200s. We also identify several episodes of immigration. Formation of aggregated settlements, which we term community centers, is positively correlated with increasing population and the time elapsed in each settlement cycle,and it persists during periods of regional population decline, but it does not correlate with climatic variation averaged over periods. Architectural and land-use practices depleted pinyon-juniper woodlands during the first cycle, but more stable field systems and greater recycling of construction timber resulted in more sustainable management of wood resources during the second cycle, despite much higher population densities. Our estimates for maize production are lower than previous estimates, especially for the A.D. 1200s, when population reached its peak in the study area. Even so, considerable potential agricultural production remained unused in the decades that immediately preceded the complete depopulation of our study area.
New archaeological research and computer modeling suggest why Ancestral Puebloans deserted the northern Southwest United States.
We review a suite of agent-based models developed by the Village Ecodynamics Project (VEP) to study ecological, economic, social, and political processes among prehispanic Puebloan (“Anasazi”) populations in the Northern US Southwest in the context of a dynamic natural environment. Collectively these models shed light on processes that include the local intensification of turkey raising, the emergence of complex societies in this region, and the complete depopulation of the Northern Southwest in the thirteenth-century AD. Quantitative computational modelling contributes to the explanatory goals of a scientific archaeology and such models should eventually provide standards allowing for more rigorous comparison of distinct archaeological sequences.
We present an agent-based model for voluntaristic processes allowing the emergence of leadership in small-scale societies, parameterized to apply to Pueblo societies of the northern US Southwest between AD 600 and 1300. We embed an evolutionary public-goods game in a spatial simulation of household activities in which agents, representing households, decide where to farm, hunt, and locate their residences. Leaders, through their work in monitoring group members and punishing defectors, can increase the likelihood that group members will cooperate to achieve a favorable outcome in the public-goods game. We show that under certain conditions households prefer to work in a group with a leader who receives a share of the group’s productivity, rather than to work in a group with no leader. Simulation produces outcomes that match reasonably well those known for a portion of Southwest Colorado between AD 600 and 900. We suggest that for later periods a model incorporating coercion, or inter-group competition, or both, and one in which tiered hierarchies of leadership can emerge, would increase the goodness-of-fit.
The Mesa Verde Community Center Survey (MV-CCS) is a multi-year field project that seeks to expand our understanding of the distribution and organization of large, ancestral Pueblo villages in Mesa Verde National Park (MVNP) that were occupied from AD 600-1290. The 2011 survey focused on characterizing the distribution of community centers (large, aggregated Pueblo villages) in Little Soda Canyon, and on completing documentation for those visited during the 2009 season. We delimited four community centers in the upper reaches of Soda Canyon: 1) the 34-plex excavated by Deric O’Bryan in the late 1940s; 2) the 34-plex Isolated Great Kiva; 3) Juniper Flats; and 4) Battleship Rock. Our fieldwork involved synthesizing the existing archaeological documentation done by NPS archaeologists during the Chapin V post-fire assessment to produce composite maps of these villages in order to better understand their cultural landscape. We also analyzed the pottery found on these sites to determine occupation histories of the villages (N sherds). This research is part of the National Science Foundation-funded “Village Ecodynamics Project II”, or VEP II, which is a multi-disciplinary project that seeks to understand the changing relationships between Pueblo societies and their environments.
The Mesa Verde Community Center Survey (MV-CCS) is a multi-year field project that seeks to better understand the distribution and organization of large, ancestral Pueblo villages in Mesa Verde National Park (MVNP) that were occupied from AD 600–1290. It is a component of the National Science Foundation-funded “Village Ecodynamics Project II”, or VEP II, which is a multi-disciplinary project that studies the changing relationships between Pueblo societies and their environments. We have spent three field seasons documenting community centers (2009, 2011, and 2012) and have conducted fieldwork at 13 of the largest, aggregated villages in Mesa Verde National Park. For each community center, we produced a composite map of the village that synthesizes the existing archaeological documentation done by NPS archaeologists in order to better understand their cultural landscape. We also conducted in-field pottery analysis to augment existing data and to determine occupation histories of the villages
Entering Second Phase
The first phase of this project, VEP I, was focused on an 1800-sq-km window of the central Mesa Verde region in Colorado. We are currently working on a final report on that project, to be submitted to the University of California Press, and all of our publications through 2009 result from VEP I research.
In January 2009 we began the Village Ecodynamics Project II, which more than doubles the area under examination in southwestern Colorado and adds a comparative window in the northern Rio Grande region of New Mexico that stretches from the southern border of Bandelier National Monument north to the Chama valley. Fieldwork for this project begins in summer 2009 in Mesa Verde National Park. Some early results from this new round of research were reported at the 75th Society for American Archaeology meetings in St. Louis in 2010 and can be seen under the Presentations tab of this page.