The Andes mountains run parallel to the Pacific Ocean, dividing the country into three geographic regions. The costa (coast), to the west, is a narrow plain, largely arid except for valleys created by seasonal rivers. The sierra (highlands) is the region of the Andes; it includes the Altiplano plateau as well as the highest peak of the country, the 6,768 m (22,205 ft) Huascarán. The third region is the selva (jungle), a wide expanse of flat terrain covered by the Amazon rainforest that extends east. Almost 60% of the country's area is located within this region.
Most Peruvian rivers originate in the peaks of the Andes and drain into one of three basins. Those that drain toward the Pacific Ocean are steep and short, flowing only intermittently. Tributaries of the Amazon River are longer, have a much larger flow, and are less steep once they exit the sierra. Rivers that drain into Lake Titicaca are generally short and have a large flow. Peru's longest rivers are the Ucayali, the Marañón, the Putumayo, the Yavarí, the Huallaga, the Urubamba, the Mantaro, and the Amazon.