Wallingford-Back Mine

The feldspar and quartz deposit that was to become, for a time, the biggest mine of its kind in North America was first discovered by an unnamed prospector who, according to the legend, sold his discovery to George Wallingford for a bag of potatoes. 

While the tale of the prospector and the potatoes is not confirmed, it is known that Mr. Wallingford sold the rights to the site to the Canadian Flint and Spar company for $12,000. The company began exploiting the mine in 1924 before being acquired by Consolidated Feldspar in 1939, and acquired again by the International Minerals and Chemical Corporation later on. With all of the buying and re-buying, the mine eventually grew to be the largest mine in North America, pulling an estimated 225,000 tons of feldspar and 150,000 tons of quartz from the ground. The site was mined for its precious minerals continuously until 1972, when it was finally closed, leaving behind a series of pits, caverns, and holes to be retaken by nature.

Today the former mine site is open to the public and is a stunning (semi)natural location. In order to get to the minerals, the Wallingford-Back Mine hollowed out an entire hill creating a stone cathedral with huge rock pillars holding up the ceiling. In addition, the flooded lower parts of the mine, which can be swam in, are also piercing blue thanks to the remaining quartz. 

Update April 2018: It's no longer open to the public.