Columbia subject headings:
Coal mines and mining--Rocky Mountains Region--History.
Mine safety--Law and legislation--Rocky Mountains Region.
Mine safety--Rocky Mountains Region--History.
Harvard subject headings:
Coal mines and mining--Rocky Mountains Region--History.
Mine safety--Law and legislation--Rocky Mountains Region.
Mine safety--Rocky Mountains Region--History.
Princeton subject headings:
Coal mines and mining--Rocky Mountains Region--History.
Mine safety--Law and legislation--Rocky Mountains Region.
Mine safety--Rocky Mountains Region--History.