Panama is a country of heavily forested hills and mountain ranges. The two principal ranges are in the eastern and western sections of the country, and a third, minor range extends southward along the Pacific coast into Colombia. The eastern Cordillera de San Blas parallels the Caribbean coastline, while the Serranía de Tabasará ascends westward, culminating in the Barú volcano (3,475 m/11,401 ft), formerly known as Chiriquí. Between these ranges, the land breaks into high plateaus, ridges, and valleys. The Panama Canal utilizes a gap in these ranges that runs northwest to southeast and averages only 87 m (285 ft) in altitude. Panama has more than 300 rivers, most of which flow into the Pacific, with only the Tuira River in Darién Province of any commercial importance. Both coasts of the isthmus have deep bays, but the Gulf of Panama is especially well provided with deepwater anchorages. Panama also has more than 1,600 islands, including the Amerindian-inhabited San Blas Islands in the Caribbean (366) and the Pearls Archipelago (Archipiélago de las Perlas) in the Gulf of Panama (over 100). Its largest island is the penal colony Coiba, which is south of the Gulf of Chiriquí.