Zaire occupies the heart of the Congo River basin, which comprises about three-fifths of the nation's total area. The cuvette a major depression in the northwestern quarter of the nation, is formed as the Congo River turns from its northerly course to arch west above the Equator, then turns southwestward toward the Atlantic Ocean. High plateaus rise in every direction from the central basin. In the northeast and east they rise to elevations between 3,000 and 4,000 feet before merging with the Mitumba Mountains at the western rim of the Rift Valley and rising above 16,000 feet in the Ruwenzori Range astride the Ugandan border in the northeast. The plateaus to the south and southeast culminate in the mountain peaks of Shaba Plateau, rising to 5,250 feet in the extreme southeast between Zambia and Tanzania. At Zaire's narrow strip of Atlantic coast the Congo River empties into the sea.