The use of mortar and pestles has long been associated with acorn processing in California. Based on ethnographic and archaeological evidence, groundstone was used to process a multitude of resources, including small mammals. Twenty groundstone artifacts recovered from the Rock Camp Site in the San Bernardino Mountains were analyzed for protein residues using the crossover immunological electrophoresis (CIEP) method. Using previously obtained data from the Summit Valley, a comparative analysis was done to determine if processing small mammals on groundstone was a common occurrence throughout the San Bernardino Mountain region.