Amazon Rain forest, large tropical rain forest occupying the drainage basin of the Amazon River and its tributaries in northern South America and covering an area of 2,300,000 square miles (6,000,000 square km). Comprising about 40 percent of Brazil’s total area, it is bounded by the Guiana Highlands to the north, the Andes Mountains to the west, the Brazilian central plateau to the south, and the Atlantic Ocean to the east.