Columbia subject headings:
Harvard subject headings:
Industries--Mexico--Piedras Negras Region.
Mexican-American Border Region--Economic conditions.
Piedras Negras Region (Mexico)--Commerce.
Piedras Negras Region (Mexico)--Population.
Tourism--Mexico--Piedras Negras Region.
Princeton subject headings:
Industries--Mexico--Piedras Negras Region.
Mexican-American Border Region--Economic conditions.
Piedras Negras Region (Mexico)--Commerce.
Piedras Negras Region (Mexico)--Population.
Tourism--Mexico--Piedras Negras Region.