The mining of tin, copper and other metals was the mainstay of the Cornish economy from prehistoric times until the late twentieth century when it became uneconomic. Cornish mining expertise went all over the world. Today a prominent feature of the landscape are the ruins of chimneys, engine houses, railways and tramways that serve as a memorial to the thousands of miners who down the ages dug the vertical shafts and toiled underground or on the surface to win precious metal from the ore-bearing granite. In 2006 UNESCO accorded World Heritage Site status to several Cornish and West Devon mining landscapes.