Geologic map and cross section of the Abra quadrangle, Costa Rica - Castillo Muñoz, Rolando 1937- (Department of the Interior, United States Geological Survey, 1977)
"Prepared in cooperation with the Oficina de Defensa Civil and the Direccion de Geología, Minas y Petróleo, Ministerio de Industria y Comercio under the auspices of the Governmentof Costa Rica and the Agency for International Development, U.S. Departement for State"