Mapping NJ’s Hundreds of Abandoned Mines

The sinkholes that opened along Route 80 in Morris County shocked many, but given the rich mining history of the area, they might not be surprising.

A New Jersey Geological Survey history of the New Jersey Highlands notes that the formation of the region over a billion years led to its rocky characteristic, with granite underlying about half of the area that stretches like a sash from northern Bergen County down to western Hunterdon County. The rocks were rich in mineral deposits, most notably the iron ore magnetite that was mined for more than two centuries.