Temporal Variation in Obsidian Procurement in the Northern Rio Grande and Its Implications for Obsidian Movement into the San Juan Area

Arakawa and colleagues (2011) use temporal changes in obsidian source patterns to link the late thirteenth-century abandonment of the Mesa Verde region to Ortman's (2010, 2012) model of Tewa migration to the northern Rio Grande. They employ Anthony's (1990) concept of reverse migration, inferring that an increase in Mesa Verde–region obsidian from a specific Jemez Mountain source reflects the scouting of an eventual migration path. Weaknesses of this inference are that only obsidian data from the Mesa Verde region were used in its development and that the model does not consider the complexities of previously documented patterns of settlement and stone raw material use in the northern Rio Grande. By examining source data from parts of northwestern and north-central New Mexico, we find that the patterning seen in the Mesa Verde obsidian data is widespread both geographically and temporally. The patterns are more indicative of a change in acquisition within a down-the-line exchange system than a reverse migration stream. Population trends on the southern Pajarito Plateau, the probable source of the acquisition change, suggest ancestral Keres rather than Tewa involvement in thirteenth-century obsidian distribution.

Common Goods in Uncommon Times: Water, Droughts, and the Sustainability of Ancestral Pueblo Communities in the Jemez Mountains, New Mexico, AD 1100-1700

Adapting our infrastructure and institutions to climate change is a crucial dilemma for modern society. Archaeologists should be well positioned to address this issue with examples from the past. Yet, too often when we find that cultural changes are synchronous with climate variation, such as abandonment of a region during a drought, we advance causal arguments to what may merely be correlations. I argue that identifying proxies for resource management in the archaeological record, particularly for resources managed by collective action and vulnerable to climate change, can help to address this problem. To test this approach I studied water management practices of Ancestral Pueblo communities living on the highland mesa-tops of the Jemez Mountains of New Mexico. Between AD 1100-1700 cultural histories across this region diverged. Ancestral Towa communities of the Jemez Plateau sustained high populations until Spanish removal in the 17th century. The adjacent Pajarito Plateau was nearly completely depopulated by ancestral Tewa and Keres communities by the early 16th century. Archaeologists hypothesize that droughts were a factor in pushing people off the Pajarito Plateau, yet the endurance of communities on the Jemez Plateau is unconsidered. Mesa-top communities in both regions constructed artificial water reservoir features, which historical Pueblo communities managed as common pool resources. I hypothesize that these archaeological features reflect collective action decision-making for managing water, a resource vulnerable to scarcity on these mesa-tops during droughts, and that decisions made about water management influenced the long-term sustainability of Ancestral Pueblo communities. Through diachronic socio-hydrological modeling, I identify how climate variation influenced feedbacks between resource users, water infrastructure, and hydrological systems. I conducted modeling of paleohydrological system responses to droughts, direct geoarchaeological investigations of fifteen reservoirs at nine Ancestral Pueblo villages, and geospatial analyses of water access. My hydrological modeling found that the Pajarito Plateau is more vulnerable to hydrological droughts than the Jemez Plateau. My geoarchaeological investigations found that communities on the Jemez Plateau built reservoirs before droughts when populations were low, and that reservoirs were used and maintained through their entire occupation histories. By contrast, communities of the Pajarito Plateau built reservoirs in the early 1300s when hamlets were coalescing into villages at the peak of regional populations. All of the reservoirs on the Pajarito Plateau, as well as many of the villages with reservoirs, were then abandoned by the mid-1400s. Through least cost analyses from hundreds of water sources to thousands of archaeological sites I found that water costs became much higher during droughts on the Pajarito Plateau, which was further exacerbated by the pooling of resources (and risks) in aggregated communities. Therefore, it cannot be ruled out that an over-reliance on collective action approaches to water management made communities on the Pajarito Plateau more vulnerable to hydrological droughts than communities on the Jemez Plateau. My work shows how archaeological research into resource management, employing earth science methods and common pool resource theory, contributes to dialogs surrounding adaptations to climate change.

Obsidian Evidence of Interaction and Migration from the Mesa Verde Region, Southwest Colorado

A growing body of evidence demonstrates that ancestral Pueblo people living in the central Mesa Verde region of the U.S. Southwest maintained long-distance contacts with other Pueblo peoples. Questions of Pueblo interactions through time and across space have traditionally been addressed using ceramic sourcing data. This research uses obsidian source data to argue that, from A.D. 600 to 920, residents of the central Mesa Verde region obtained obsidian from throughout the U.S. northern Southwest, but that from A.D. 1060 to 1280 they acquired obsidian almost exclusively from the Jemez Mountains area of north-central New Mexico. In addition, importation of obsidian from the Pajarito Plateau increased during the period of population decline in the Mesa Verde region, and population expansion on the Pajarito. Characteristics of the obsidian assemblage from central Mesa Verde region sites also suggest that Jemez obsidian entered the region primarily in the form of finished arrows, arrow points, and arrow-point preforms. We argue that these patterns reflect return migration by early immigrants from the Mesa Verde region to the northern Rio Grande, an early stage in the development of a migration stream between the two regions.