Statement of Significance (as of designation - July 4, 1961):
Santa Clara Indians had used cinnabar from this site long before 1824, when information provided by them led Mexican settlers to the first quicksilver deposits identified in North America. Europeans used the mercury in the ore to facilitate the mining of gold and silver. The site was named after the world's greatest quicksilver mine, Almaden, in Spain. Mercury from New Almaden's mines was essential to the mining process during the gold rush.