126-6 Geoarchaeology of Cedros Island’s Southern End: A Late Pleistocene to Early Holocene Case Study

Session: Geoarchaeology of Sites to Landscapes: Current Research on Long-Term Water and Soil Management and Maladaptation, Part II

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Geoarchaeological research on the southern end of Cedros Island, Baja California, Mexico, reveals that local hydrological and geological conditions played a critical role in preserving some of the oldest evidence for coastal foraging in North America. At three stratified sites—El Peregrino, Colina Castor, and Cerro Pedregoso—archaeological materials dating between ~12,900 and 9600 cal BP are preserved in inland contexts associated with now-extinct freshwater springs. These deposits offer a rare terrestrial record of early marine-oriented lifeways that in most coastal regions would have been submerged or destroyed by postglacial sea-level rise. The key to this preservation lies in Cedros Island’s unique bedrock structure, where freshwater aquifers formed at contacts between the Cedros and Valle Formations. These spring zones sustained surface water flow during wetter Late Pleistocene climates and served as ecological oases in an otherwise arid landscape. Early foragers appear to have targeted these freshwater sources, transporting marine foods and other resources inland from coastlines that lay 10–15 kilometers away. At El Peregrino and Colina Castor, Bayesian modeling of more than 40 radiocarbon ages confirms occupation during the Younger Dryas despite the effects of floralturbation. At Cerro Pedregoso, radiocarbon-dated cultural materials span ~12,000 to 9600 cal BP, and a buried paleosol below these deposits suggests the potential for even earlier occupation. These findings underscore how the patterned association of spring formations, terrain morphology, and sedimentation processes, particularly the combined action of colluvial slopewash and aeolian input, creates conditions favorable for both repeated human use and long-term archaeological preservation. Recognizing this interplay provides a replicable geoarchaeological framework for predicting where other early coastal occupations may be found. Future investigations that focus on similar spring-fed landforms elsewhere on Cedros Island, especially in areas where geomorphic conditions promote gradual burial, are likely to yield new Pleistocene-aged sites and contribute significantly to our understanding of the earliest coastal lifeways in the Americas.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8550

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