The arrastra has been used since the Phoenicians to grind ores, most often gold or silver. The construction involves a circular pit paved with flat stones. Large flat-bottomed drag stones are connected to a center post by a long arm. Using horse, mule or human power, the arm drags the large stones over the ore, crushing it. This arrastra at the Gold Bug Mine was powered by a waterwheel, clearly evident in the photograph. It is a cheap but effective...