From Marshland to Desert: The Late Prehistoric Environment of Boca de Potrerillos,Nuevo León,Mexico

Despite the paucity of archaeological research in the Sierra Madre Oriental ecotone of northeastern Mexico, a patterned distribution of large open campsites replete with petroglyphs is suggested by a recent rock art survey sponsored by the Mexican government. Pilot research at Boca de Potrerillos, one of the largest and best preserved examples of this site type, demonstrates that the intermontane desert of today was once a combination of grassland and wetland. Hundreds of hearths are now exposed on the surface of a desiccated alluvial plain and thousands of petroglyphs have been incised into sandstone boulders fringing the occupational area. Radiocarbon assay of charcoal derived from buried hearths dates the intact subsurface living surfaces to the period between 1350 and 650 years ago. Pollen and phytolith samples from buried strata and ground stone implements describe a mesic environment and provide a list of potential economic plants processed at the site. The presence of both aquatic and terrestrial snails supports the paleoenvironmental reconstruction of wetlands, replete with emergent vegetation, flanked by rocky slopes. Archival research suggests that a drying trend is mirrored in the agricultural history of the valley but the extreme degradation effected in the last four decades is attributable to modern exploitation of the aquifer.