One of the largest iron mining regions in Adirondack Park is around the town of Moriah, near Lake Champlain. In the 1870s underground mines here produced close to ten percent of iron ore in the USA, supplying the iron works at Troy, New York, and beyond. The mines were underground, and accessed through a number of shafts over the years. One exception was where the ore body was closest to the surface, at Open Pit 21, now a flooded pond behind a fence between the communities of Mineville and Witherbee. Mines operated until the 1970s. The former prosperity of the region is evident in some of the remaining architecture, such as Memorial Hall which was built for the miners in Mineville, across from the offices of the Witherbee-Sherman Mining Company, the company that developed and operated the mines.