Columbia subject headings:
Landscapes--United States.
Mines and mineral resources--United States--Pictorial works.
Mines and mineral resources--United States.
Harvard subject headings:
Mines and mineral resources--United States--History.
Mines and mineral resources--United States--Pictorial works.
Princeton subject headings:
Mines and mineral resources--United States--History.
Mines and mineral resources--United States--Pictorial works.