Cauca, a large coast department of Colombia, South America, lying between the departments of Bolivar, Antioquia, Caldas and Tolima on the E., and the Pacific Ocean and Panama on the W., and extending from the Caribbean Sea S. to the department of Nariño. Pop. (1905, estimate) 400,000; area 26,930 sq. m. Although Cauca was deprived of extensive territories on the upper Caquetá and Putumayo, and of a large area bordering on Ecuador in the territorial redistribution of 1905, it remained the largest department of the republic. The Western Cordillera, traversing nearly its whole length from south to north, and the Central Cordillera, forming a part of its eastern frontier, give a very mountainous character to the region. It includes, besides, the fertile and healthful valley of the upper Cauca, the hot, low valley of the Atrato, and a long coastal plain on the Pacific. The region is rich in mines and valuable forests, but its inhabitants have made very little progress in agriculture because there are not adequate transportation facilities. The capital of the department is Popayán at its southern extremity, with an estimated population in 1905 of 10,000, other important towns are Cali (16,000), Buga, Cartago and Buenaventura.