Colorado is dotted with old gold mines all over the state. The abandoned ones can be pretty dangerous from what I've heard (toxic gases, deep water, etc). I'm sure there's lots of gold still in the mountains. read more
Lost mines are a popular form of lost treasure legend. The mine involved is usually of a high-value commodity such as gold, silver or diamonds. Often there is a map (sometimes called a "waybill") purportedly showing the location of the mine. read more