Columbia subject headings:
Calumet Region (Ill. and Ind.)--Economic conditions.
Iron industry and trade--Calumet Region (Ill. and Ind.)
Steel industry and trade--Calumet Region (Ill. and Ind.)
Harvard subject headings:
Calumet Region--Economic conditions.
Iron industry and trade--Calumet Region (Ill. and Ind.)
Steel industry and trade--Calumet Region (Ill. and Ind.)
Princeton subject headings: