Archaeologists have long recognized the central importance of interregional relationships in much of Andean prehistory, but consistent forms of evidence that can be used to gauge long-distance interaction are relatively limited. Over the past century, systematic studies on a regional scale have provided evidence of interaction based on stylistic attributes, such as the presence of non-local ceramics, design elements, and architectural styles. More recently, geochemical evidence has taken a more prominent role in documenting long-distance interaction and exchange because evidence from a variety of chemically unique materials - such as obsidian - have been accumulating in databases as chemical identification techniques are refined. This project aims to apply geochemical evidence of long-distance interaction from an obsidian source in the south-central Andes to an interpretation of regional developments.

Obsidian is among the least-perishable of a number of materials that were widely transported in the prehispanic Andes. On one level, obsidian should be understood as just another one of the widely circulated items, such as nuts, gourds, wood, shell, metal, coca, sebil, and basalt, in a list that is immeasurably long. As a regionally distributed material, however, obsidian has a number of characteristics that are distinctive from some of other goods that circulated in local and regional trade. As a lithic raw material, obsidian is a reductive technology and therefore distance decay effects are prominent in its regional distribution. Obsidian implements can have extremely sharp edges, and by far the most common formal obsidian tools produced in the south-central Andes were the projectile points. Obsidian artifacts are sometimes found in contexts - such as monuments or burials, that suggest that obsidian had ritual importance - however, throughout the region obsidian artifacts are frequently encountered in domestic contexts and middens with little compelling evidence of ritual or symbolic importance. A central concern of this research project is to avoid the simplistic, dichotomous archaeological construction of a "utilitarian" artifact group versus a "prestige" and/or "ritual" associated artifact group. As a highly visible material that was often made into projectile tips, "utilitarian" obsidian tipped implements themselves may have had a role in social influence or coercion, and were perhaps used in status competition displays. Obsidian made into a sharp weapon simultaneously represents access to non-local goods and, in the case of non-local obsidian, may reflect regional scale alliances. Thus, the circulation of obsidian may have been akin to that of utilitarian products, a such as salt, or along the lines of a precious commodity like gold or turquoise where value is related to production costs and reflects scarcity or exclusivity.

Figure 1-1. Larger study region with modern towns and roads. General obsidian distribution areas are depicted, showing largely a Formative Period extent.

Archaeologists identify these materials as non-local when they are encountered in archaeological sites far from their source areas, and in these contexts archaeologists interpret non-local materials are seen as providing evidence of the long distance movement of goods. The dramatic altitudinal zonation on the flanks of the Andes contributes to the archaeological identification of non-local materials because a number of these products are zone-specific. The major environmental and geological zones with distinctive products include the Amazonian lowlands to the east, the mineral rich western Cordillera, and the pacific littoral.

This project focuses on the source region of an obsidian type that was widely circulated in the prehispanic Andes. This chemical group, first referenced in the 1970s as the "Titicaca Basin Type" (Burger and Asaro 1977), was finally traced to its geological source in the Colca valley of Arequipa, Peru in the 1990s. In the Colca, the geochemical type was documented under two names, the Chivay Source (Burger, et al. 1998) and the Cotallalli Source (Brooks, et al. 1997). The source lies in volcanic terrain that is relatively difficult to access by the modern road network, a situation which has hampered research in this zone but has also resulted in relatively little disturbance to archaeological sites in the obsidian source area. This project sought to comprehensively research this zone in order to address a number of long-standing theoretical questions concerning the human use of obsidian in the larger region. Obsidian from the Chivay source is found in a variety of archaeological contexts in the region ranging from common residential middens to ceremonial structures and burials. Unlike other regions of the world where a variety of artifact forms are produced from obsidian, in the south-central Andes the formal implements made from obsidian are largely restricted to projectile points. Simple obsidian flakes are seen as valuable as well, as the shearing and butchering requirements of dedicated pastoralists are significant, and these sharp obsidian flakes filled a functional category akin to razor blades in modern life.

On a theoretical level, this research can contribute to anthropological models concerning the emergence of social hierarchy, the influence of regularized caravan-based trade, and the role of exchange in non-local goods that were widely-circulated in prehistory. Obsidian escapes easy classification as a "prestige item" or an "ordinary good" because the cultural meaning of the material appears to have been highly variable. Obsidian is typically abundant at archaeological sites close a geological source and scarce in areas more distant from geological sources, and obsidian flakes are plentiful at pastoralist rock shelter sites in the altiplano that appear to be relatively lacking in other material goods. Together with coca leaf and other widely circulated goods of cultural value in the Andes, obsidian appears at times in ritual contexts; for example, obsidian may be used as a knife used in a llama sacrifice, as flakes placed in a burial, or as projectile point tips represented on Tiwanaku and Nasca ceramics. However, obsidian appears to not have been a "preciosity" in the sense that large and recognizable quantities of labor were necessarily invested in the production of the material, and indeed obsidian is often found in commonplace, utilitarian contexts. As a household level enterprise, the acquisition of obsidian may constitute evidence of regional interaction which contributes to an archaeological understanding of the prehistoric emergence of regularized exchange over distance, perhaps scheduled around festivals, seasonal harvests, and other regional scale events that integrated distant communities across the Andean highlands. In sum, while it is difficult to place obsidian on a scale from ordinary to prestige good, it appears that the mere possession obsidian may have had some value as a symbol of participation in the long-distance exchange of a variety of goods of cultural value.

This project investigates the economy of Chivay obsidian in prehistory at three levels. First, fieldwork was conducted at the Chivay source in order to examine production at the obsidian source area itself. This work documented the geological exposures of the material, the archaeological sites in association with the source area, and the physical geography and trail system around the source. Second, the project area included obsidian consumption zones within a day's walk of the source in two adjacent residential areas in order to evaluate the local use of obsidian within the larger archaeological context of the Upper Colca. Third, the regional consumption patterns of Chivay obsidian in the south-central Andes were explored using existing studies from the published sources for a more complete picture of production, distribution, and consumption of the material through prehistory. This dissertation represents the integration of these three perspectives on Chivay obsidian in light of anthropological theories of exchange and Andean culture history.

Archaeological evidence for interpreting obsidian production at Chivay takes the form of differences in diagnostic materials and artifact morphology across space from a surface survey, and from measurable change in stratified deposits from test excavations. Four models of procurement and circulation are proposed here, and the material correlates for these models are evaluated based on expectations and measurable changes in artifacts that primarily consist of flakes and cores. The information potential from surface scatters is limited by the non-diagnostic nature of most artifacts at raw material quarries. Nevertheless, this research has found that a strong correlation exists between obsidian intensification and early pastoralism, and perhaps camelid caravan transport; and the research contributes to answering long-standing questions about the relationship between the Colca valley and prehispanic Titicaca Basin polities. This study explores obsidian production and circulation as a unifying theme that can be studied at a regional scale in order to examine long-term processes that led to social changes manifested in the emergence of chiefdoms and states in the Andes.