Studies of local forms of social organization in peripheral areas can enrich our understanding of the sociopolitical factors structuring core-periphery interactions. This research explores how local group identities impacted the ways in which individuals and communities at San Pedro de Atacama, Chile, expressed their relationship to the Tiwanaku polity during the Middle Horizon. Combining information from body modification practices, burial contexts, and isotopic indicators of diet and geographic origin, we demonstrate that differential incorporation of Tiwanaku goods and practices may have served alongside other local customs to mark social group distinctions between individuals interred in the Solcor 3 and Solcor Plaza cemeteries.Key words: Bioarchaeology, carbon, oxygen and strontium isotopes, cranial vault modification, mortuary practices, social differentiation, Middle Horizon, Tiwanaku. Estudios de las formas locales de organización social en zonas periféricas pueden enriquecer nuestra comprensión de los factores sociopolíticos que estructuran las interacciones entre centro y periferia. Esta investigación explora cómo las identidades de grupos locales de San Pedro de Atacama, Chile, influyeron en la manera como los individuos y las comunidades expresaron su relación con el Estado de

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These results indicate greater reliance on marine resources at Armatambo versus Rinconada Alta, supporting the ethnohistoric model of socioeconomic specialization for the Central Andean coast. Deviations from large-scale dietary trends suggest complexities not accounted for by the ethnohistoric model, including intra-community subsistence specialization and/or variation in resource access.

The analysis of 87 Sr/ 86 Sr has become a robust tool for identifying non-local individuals at archeological sites. The 87 Sr/ 86 Sr in human bioapatite reflects the geological signature of food and water consumed during tissue development. Modeling relationships between 87 Sr/ 86 Sr in human environments, food webs, and archeological human tissues is critical for moving from identifying non-locals to determining their likely provenience. In the Andes, obstacles to sample geolocation include overlapping 87 Sr/ 86 Sr of distant geographies and a poor understanding of mixed strontium sources in food and drink. Here, water is investigated as a proxy for bioavailable strontium in archeological human skeletal and dental tissues. This study develops a water 87 Sr/ 86 Sr isoscape from 262 samples (220 new and 42 published samples), testing the model with published archeological human skeletal 87 Sr/ 86 Sr trimmed of probable non-locals. Water 87 Sr/ 86 Sr and prediction error between the predicted and measured 87 Sr/ 86 Sr for the archeological test set are compared by elevation, underlying geology, and watershed size. Across the Peruvian Andes, water 87 Sr/ 86 Sr ranges from 0.7049 to 0.7227 (M = 0.7081, SD = 0.0027). Water 87 Sr/ 86 Sr is higher in the highlands, in areas overlying older bedrock, and in larger watersheds, characteristics which are geographically correlated. Spatial outliers identified are from canals, wells, and one stream, suggesting those sources could show non-representative 87 Sr/ 86 Sr. The best-fit water 87 Sr/ 86 Sr isoscape achieves prediction errors for archeological samples ranging from 0.0017-0.0031 (M = 0.0012, n = 493). The water isoscape explains only 7.0% of the variation in archeological skeletal 87 Sr/ 86 Sr (R 2 = 0.07), but 90.0% of archeological skeleton 87 Sr/ 86 Sr fall within the site isoscape prediction ± site prediction standard error. Due to lower sampling density and higher geological variability in the highlands, the water 87 Sr/ 86 Sr isoscape is more useful for ruling out geographic origins for lowland

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