Experimental hearths and the thermal alteration of caliche on the Southern High Plains

Throughout the Holocene, caliche has been a ubiquitous technological resource for the people of the Southern High Plains. Achaeological sites on the Southern High Plains often contain thermal features that appear to utilize caliche nodules in vaious cultural processes. These processes usually involve some degree of thermal dynamic alteration to the caliche, identified in the archaeological record as fire-scorched or blackened nodules. Previous studies of the pyrodynamic properties of caliche have focused on quantification of color and fracture patterns within a laboratory setting, without direct involvement of cultural processes or problems associated with thermal features. Thermal alteration variables of caliche are examined from an actualistic perspective, utilizing previously excavated basin feature geometry and local caliche outcrops. Results indicate that sustained, intense heating of caliche (above 204°C) causes significant, but variable, structural transformations at the specimen level. The experimental use of shallow basin hearths demonstrates that hearth structures were easily capable of achieving and sustaining temperatures that would result in the physical alteration of individual caliche nodules, defined here as hearthstone. The broader implications of this study suggest that the interpretation of archaeological heartstone assemblages should reflect variability, as observed during this experiment.