The primary focus of this research is the poorly understood relationship between water insufficiency and broad-scale social change, in the semi-arid lower Salt River Valley, in central Arizona. The overarching research question guiding this research is if water insufficiency could have prompted sociopolitical change among the Hohokam. Specifically, the research investigates if long-term water deficits were a catalyst for the two most consequential transformations in Hohokam history – the Preclassic/Classic transition (A.D. 1070-1100/1150) and the early to late Classic period transition (ca. A.D. 1300).

This research used extensive historical aerial photographs and cultural resource management excavation data to complete the largest-scale reconstruction of Hohokam irrigation. These lines of evidence provided exceptional insight into the developmental histories of eight major irrigation systems along the lower Salt River, four of which are newly defined here. Also, historic Salt River streamflow trends are leveraged to refine previously reconstructed annual flow discharges. The irrigation system reconstruction provided the means for estimating irrigation demand through irrigated acreage, and monthly streamflows supplied the amount of water available during key points in the two agricultural cycles per year. Together, irrigation demand and water availability provided necessary data to identify persistent water shortages during Hohokam history between A.D. 740 and 1450.

The findings discussed in this dissertation demonstrate that water insufficiency likely had no notable effect related to either the Preclassic/Classic or early to late Classictransitions in the lower Salt River Valley. Instead, there was possibly enough water through time for Hohokam farmers to meet agricultural demands. Three substantial additional insights were gained from this research. First, an extremely large flood, occurring either during the late Colonial or early Sedentary periods, may have profoundly altered irrigation agriculture and social organization in the valley. Second, during at least the Sedentary and Classic periods, Hohokam irrigation was structured into standardized irrigation units (SIU), a far more complex and efficient method of irrigation than previously perceived along the lower Salt. Third, a bedrock reef located near Canal System 2, and not at other lower Salt irrigation systems, is plausibly a determinate in Canal System 2’s longevity.

In the proposed project I simultaneously and reflexively identify and characterize social boundaries in the archaeological record by examining material culture distributions in novel ways to re-assess the scale of the Verde Confederacy, a proposed regional-scale multi-settlement alliance in Late Prehistoric central Arizona. I focus on boundaries between entities larger than villages, but smaller than regions or culture areas. I propose three innovations to better accomplish these goals. First, unlike previous conceptualizations of social boundaries as monolithic, I argue that they are better conceived of as a heterogeneous, multi-faceted phenomenon. Second, I investigate social boundaries by examining multiple lines of evidence. Previous researchers have tended to focus on one category of data at the expense of others. Third, I associate boundaries with relational and categorical collective social identification. An alliance requires regular collective actions including communication and coordinated action between large groups. These actions are most likely to emerge among groups integrated by relational networks who share a high degree of categorical homogeneity.

I propose a plain ware ceramic provenance model. Seven reference groups represent ceramic production in specific geographic areas. The reference groups are mineralogically and geochemically distinct, and can be visually differentiated. With this provenance model, I reconstruct the organization of utilitarian ceramic production and exchange, and argue that plain ware distribution is a proxy for networks of socially proximate friends and relatives. The plain ware data are compared to boundaries derived from settlement patterns, rock art, public architecture, and painted ceramics to characterize the overall nature of social boundaries in Late Prehistoric central Arizona.

Three regions in the study area are strongly integrated by relational networks and categorical commonality. If alliances existed in Late Prehistoric central Arizona, they were most likely to emerge at this scale. A fourth region is identified as a frontier zone, where internal connections and shared identities were weaker. As seen among the League of the Iroquois, smaller integrated entities do not preclude the existence of larger social constructs, and I conclude this study with proposals to further test the Verde Confederacy model by searching for integration at a broader spatial scale.

Environmental change has often been cited as affecting choices made whether to pursue cooperative or competitive strategies. The Flagstaff region provides a unique opportunity to address how environmental changes may affect choices made between competition and cooperation. Part of the region was a prehistoric frontier zone between three archaeological cultures and these groups had to contend with a marginal and highly variable climate for agriculture. These regional patterns of climatic variation are well documented and further the eruption of Sunset Crater Volcano in the midst of this frontier zone devastated local environments and reshaped the landscape. As groups re-colonized the frontier zone, they actively sought to negotiate new boundaries using both competitive and cooperative strategies that can be discerned archaeologically, including intergroup violence and the construction and use of communal ritual architecture. Dendroclimatological data is used to identify periods of environmental change and expectations for cooperative and competitive responses to these changes are developed based on anthropological theory and ethnographic case studies. These expectations are then tested against the archaeological record. Three lines of evidence are used to assess changes in levels of competition: (1) use of defensive sites, (2) presence of skeletal trauma, and (3) emergence of specialized social roles and weapons technologies. Two lines of evidence are used to assess changes in levels of cooperation (1) use of communal ritual architecture and (2) patterns of exchange. In some cases the expected relationships between favorable conditions and evidence of increased cooperation and between unfavorable conditions and evidence of increased competition are found. However, in other cases the expectations are not supported, with local historical and cultural contingencies appearing to override environmental influences. Contrasts between patterns of cooperation and competition found in the culturally diverse frontier zone versus the patterns found in the more culturally homogenous heartland are identified that suggest greater likelihood of the emergence of conflict in settings with pre-existing contexts of social differences.

This study evaluates five different hypotheses potentially accounting for the prehistoric movement of vesicular basalt during the Hohokam occupation of the Salt-Gila Basin (ca. A.D. 700-1450): 1) direct procurement; 2) direct exchange; 3) down-the-line exchange; 4) market exchange; and 5) elite-controlled exchange. The plausibility of each hypothesis is assessed by examining the relative frequency of different vesicular basalt source types at sites as related to the geographic distance from their source; intra-site variance in vesicular basalt source type diversity; inter-site variance in vesicular basalt source type diversity; and temporal specificity and continuity in source preference. The study sample is comprised of 484 vesicular basalt artifacts recovered from nine Hohokam sites: Casa Grande, Gila Crossing, the Hospital Site, La Plaza, Las Colinas, Los Hornos, Lower Santan, Pueblo Grande, and Upper Santan. Geographic provenance data for artifacts are generated by comparing their chemical composition to a geochemical reference database composed of more than 700 vesicular basalt raw material samples from 17 different source areas in the Salt-Gila Basin. Geochemical data for both artifact and raw material samples were collected using a portable X-ray fluorescence spectrometer and a newly developed sampling procedure that provides an efficient, reliable, and nondestructive means of analysis.

The results of the hypothesis testing found that direct procurement is a possible material provisioning practice for perhaps only a small number of households in the Salt-Gila Basin; specifically those located less than 10 km from a vesicular basalt outcrop. Direct exchange is also an unlikely explanation, though it cannot be rejected outright. The other exchange hypotheses, down-the-line, market, and elite-controlled exchange, as defined in this study, are all rejected as possible explanations. From these results, a new model of Hohokam vesicular basalt provisioning practices is developed for future testing. This model posits that vesicular basalt groundstone tools were produced by specialists in a handful of locations during both the Preclassic and Classic periods, and that finished tools were acquired through workshop procurement or local distributers. The implications of these findings for understanding the organization of Hohokam domestic and political economies are also discussed.

This research explores how people's relationships with the spirits of the dead are embedded in political histories. It addresses the ways in which certain spirits were integral "inhabitants" of two social environments with disparate political traditions. Using the prehistoric mortuary record, I investigate the spirits and their involvement in socio-political affairs in the Prehispanic American Southeast and Southwest. Foremost, I construct a framework to characterize particular social identities for the spirits. Ancestors are select, potent beings who are capable of wielding considerable agency. Ancestral spirits are generic beings who are infrequently active among the living and who can exercise agency only in specific contexts. Anonymous groups of spirits are collectives who exercise little to no agency. I then examine the performance of mortuary ritual to recognize these social identities in the archaeological record. Multivariate analyses evaluate how particular ritual actions memorialized the dead. They concentrate on treatment of the body, construction of burial features, inclusion of material accompaniments, and the spaces of ritual action. Each analysis characterizes the social memories that ritual acts shaped for the spirits. When possible, I supplement analysis of archaeological data with ethnohistoric and ethnographic information. Finally, I compile the memories to describe the social identities for the spirits of the dead. In this study, I examine the identities surrounding the spirits in both a Mississippian period settlement on the Georgia coast and in several Protohistoric era Zuni towns in the northern Southwest. Results indicate that ancestors were powerful members of political factions in coastal Mississippian communities. In contrast, ancestral spirits and collectives of long-dead were custodians of group histories in Zuni communities. I contend that these different spirits were rooted in political traditions of competition. Mississippian ancestors were influential agents on cultural landscapes filled with contestation over social power. Puebloan ancestral spirits were keepers of histories on landscapes where power relations were masked, and where new kinds of communities were coalescing. This study demonstrates that the spirits of the dead are important to anthropological understandings of socio-political trajectories. The spirits are at the heart of the ways in which history influences and determines politics.

This project examines the social and economic factors that contributed to the development of a specialist-based economy among the Phoenix Basin Hohokam. In the Hohokam case, widespread dependence on the products of a few concentrated pottery producers developed in the absence of political centralization or hierarchical social arrangements. The factors that promoted intensified pottery production, therefore, are the keys to addressing how economic systems can expand in small-scale and middle-range societies. This dissertation constructs a multi-factor model that explores changes to the organization of decorated pottery production during a substantial portion of the pre-Classic period (AD 700 - AD 1020). The analysis is designed to examine simultaneously several variables that may have encouraged demand for ceramic vessels made by specialists. This study evaluates the role of four factors in the development of supply and demand for specialist produced red-on-buff pottery in Hohokam settlements. The factors include 1) agricultural intensification in the form of irrigation agriculture, 2) increases in population density, 3) ritual or social obligations that require the production of particular craft items, and 4) reduced transport costs. Supply and demand for specialist-produced pottery is estimated through a sourcing analysis of non-local pottery at 13 Phoenix Basin settlements. Through a series of statistical analyses, the study measures changes in the influence of each factor on demand for specialist-produced pottery through four temporal phases of the Hohokam pre-Classic period. The analysis results indicate that specialized red-on-buff production was initially spurred by demand for light-colored, shiny, decorated pottery, but then by comparative advantages to specialized production in particular areas of the Phoenix Basin. Specialists concentrated on the Snaketown canal system were able to generate light-colored, mica-dense wares that Phoenix Basin consumers desired while lowering transport costs in the distribution of red-on-buff pottery. The circulation of decorated wares was accompanied by the production of plainware pottery in other areas of the Phoenix Basin. Economic growth in the region was based on complementary and coordinated economic activities between the Salt and the Gila River valleys.

Understanding agricultural land use requires the integration of natural factors, such as climate and nutrients, as well as human factors, such as agricultural intensification. Employing an agroecological framework, I use the Perry Mesa landscape, located in central Arizona, as a case study to explore the intersection of these factors to investigate prehistoric agriculture from A.D. 1275-1450. Ancient Perry Mesa farmers used a runoff agricultural strategy and constructed extensive alignments, or terraces, on gentle hillslopes to slow and capture nutrient rich surface runoff generated from intense rainfall. I investigate how the construction of agricultural terraces altered key parameters (water and nutrients) necessary for successful agriculture in this arid region. Building upon past work focused on agricultural terraces in general, I gathered empirical data pertaining to nutrient renewal and water retention from one ancient runoff field. I developed a long-term model of maize growth and soil nutrient dynamics parameterized using nutrient analyses of runoff collected from the sample prehistoric field. This model resulted in an estimate of ideal field use and fallow periods for maintaining long-term soil fertility under different climatic regimes. The results of the model were integrated with estimates of prehistoric population distribution and geographical characterizations of the arable lands to evaluate the places and periods when sufficient arable land was available for the type of cropping and fallowing systems suggested by the model (given the known climatic trends and land use requirements). Results indicate that not only do dry climatic periods put stress on crops due to reduced precipitation but that a reduction in expected runoff events results in a reduction in the amount of nutrient renewal due to fewer runoff events. This reduction lengthens estimated fallow cycles, and probably would have increased the amount of land necessary to maintain sustainable agricultural production. While the overall Perry Mesa area was not limited in terms of arable land, this analysis demonstrates the likely presence of arable land pressures in the immediate vicinity of some communities. Anthropological understandings of agricultural land use combined with ecological tools for investigating nutrient dynamics provides a comprehensive understanding of ancient land use in arid regions.

The Hohokam of central Arizona left behind evidence of a culture markedly different from and more complex than the small communities of O'odham farmers first encountered by Europeans in the sixteenth and seventeenth centuries A.D. Archaeologists have worked for well over a century to document Hohokam culture history, but much about Pre-Columbian life in the Sonoran Desert remains poorly understood. In particular, the organization of the Hohokam economy in the Phoenix Basin has been an elusive and complicated subject, despite having been the focus of much previous research. This dissertation provides an assessment of several working hypotheses regarding the organization and evolution of the pottery distribution sector of the Hohokam economy. This was accomplished using an agent-based modeling methodology known as pattern-oriented modeling. The objective of the research was to first identify a variety of economic models that may explain patterns of artifact distribution in the archaeological record. Those models were abstract representations of the real-world system theoretically drawn from different sources, including microeconomics, mathematics (network/graph theory), and economic anthropology. Next, the effort was turned toward implementing those hypotheses as agent-based models, and finally assessing whether or not any of the models were consistent with Hohokam ceramic datasets. The project's pattern-oriented modeling methodology led to the discard of several hypotheses, narrowing the range of plausible models of the organization of the Hohokam economy. The results suggest that for much of the Hohokam sequence a market-based system, perhaps structured around workshop procurement and shopkeeper merchandise, provided the means of distributing pottery from specialist producers to widely distributed consumers. Perhaps unsurprisingly, the results of this project are broadly consistent with earlier researchers' interpretations that the structure of the Hohokam economy evolved through time, growing more complex throughout the Preclassic, and undergoing a major reorganization resulting in a less complicated system at the transition to the Classic Period.

The causes and consequences of stylistic change have been a concern of archaeologists over the past several decades. The actual process of stylistic innovation, however, has received less attention. This project explores the relationship between the process of stylistic innovation on decorated pottery and the social context in which it occurred in the Hohokam area of south-central Arizona between A.D. 800 and 1300. This interval was punctuated by three episodes of reorganization, each of which was characterized to varying degrees by significant shifts in ideology, economics, and politics. Each reorganization episode was also accompanied by a rapid profusion of stylistic innovation on buff ware pottery. The goal of this study was to build a framework to understand the variation in the process of innovation as a response to different incentives and opportunities perceived in the changing social environment. By bringing stylistic analyses and provenance data together for the first time in Hohokam red-on-buff studies, I investigated how the process of innovation was variously influenced by social reorganizations at three different periods of time: the 9th, 11th, and 12th centuries A.D. Four variables were used to evaluate the process of innovation at each temporal period: 1) The origin of a stylistic invention, 2) the rate of its adoption, 3) the pattern of its adoption, and 4) the uniformity of its adoption among all buff ware potting communities. To accomplish the task, stylistic innovations and provenance were recorded on over 3,700 red-on-buff sherds were analyzed from 20 sites in the Phoenix Basin. The innovation process was found to vary with each reorganization episode, but often in different ways than expected. The results revealed the complexity and unpredictability of the process of stylistic innovation among the Hohokam. They also challenged some assumptions archaeologists have made regarding the scale and extent of the changes associated with some of the reorganization episodes. The variables utilized to measure the innovation process were found to be effective at providing a composite picture of that process, and thus warrant broader application to other archaeological contexts.

This study investigates the vulnerability of subsistence agriculturalists to food shortfalls associated with dry periods. I approach this effort by evaluating prominent and often implicit conceptual models of vulnerability to dry periods used by archaeologists and other scholars investigating past human adaptations in dry climates. The conceptual models I evaluate rely on an assumption of regional-scale resource marginality and emphasize the contribution of demographic conditions (settlement population levels and watershed population density) and environmental conditions (settlement proximity to perennial rivers and annual precipitation levels) to vulnerability to dry periods. I evaluate the models and the spatial scales they might apply by identifying the extent to which these conditions influenced the relationship between dry-period severity and residential abandonment in central Arizona from A.D. 1200 to 1450. I use this long-term relationship as an indicator of potential vulnerability to dry periods. I use tree-ring precipitation and streamflow reconstructions to identify dry periods. Critically examining the relationship between precipitation conditions and residential abandonment potentially sparked by the risk of food shortfalls due to demographic and environmental conditions is a necessary step toward advancing understanding of the influences of changing climate conditions on human behavior. Results of this study support conceptual models that emphasize the contribution of high watershed population density and watershed-scale population-resource imbalances to relatively high vulnerability to dry periods. Models that emphasize the contribution of: (1) settlement population levels, (2) settlement locations distant from perennial rivers, (3) settlement locations in areas of low average annual precipitation; and (4) settlement-scale population-resource imbalances to relatively high vulnerability to dry periods are, however, not supported. Results also suggest that people living in watersheds with the greatest access to and availability of water were the most vulnerable to dry periods, or at least most likely to move when confronted with dry conditions. Thus, commonly held assumptions of differences in vulnerability due to settlement population levels and inherently water poor conditions are not supported. The assumption of regional-scale resource marginality and widespread vulnerability to dry periods in this region of the U.S. Southwest is also not consistently supported throughout the study area.