Mercer Caverns are located one mile north of Murphys in Calaveras County California. They are named after the gold prospector Walter J. Mercer who discovered the caves around 1885 and filed a claim. They were later renamed as caverns. The caverns have a large number of speleothems, stalactites, and stalagmites. Under the limestone calcite are a range of aragonite minerals that are pure CaCO3.