BARCELONA, SPAIN—A rock shelter in the Sierra de Cantabria mountains in northern Spain was repeatedly used as an animal pen some 5,000 years ago, according to a study conducted by scientists from the University of Barcelona, the University of the Basque Country, and the Spanish National Research Council. Analysis of charcoal, pollen, seeds, and other plant remains recovered during the investigation indicate that Copper Age herders held their goats and/or sheep in the rock shelter intermittently, probably to take advantage of hazelnut and acorn trees that grew in the area. “We also know thanks to the microscopic study of the sediments that every now and again they used to burn the debris that had built up, probably to clean up the space that had been occupied,” archaeologist Ana Polo-Diaz of the University of the Basque Country said in a UPI report. For more on the archaeology of Spain, go to "The Red Lady of El Mirón."