Southwardly from the above, beyond the intervening Cordillera, is the River Balsas, or Mescala, 430 miles in length. This important stream has its rise in the watershed of the central plateau, or rather the extensive slopes of the Valley of Mexico, and running with a general westerly direction between the Sierras, empties into the Pacific at Zacatula. It is navigable for a short distance. The Yaqui, discharging into Pacific waters, is 390 miles long, flowing through the Sierras of Sonora to the Gulf of California. On the littoral of the Mexican Gulf is the Panuco, which rises to the north of the Valley of Mexico, flowing thence in a great curve; and being joined by various affluents from the eastern watershed of the Sierra Madres, it discharges at the port of Tampico. The Papaloapam, also draining part of the State of Vera Cruz, empties into the Gulf near the port of the same name. From the region of the peninsula of Yucatan flow two main streams--the Usamacinta and the Grijalva--which are partly navigable. All these rivers are further described in the chapter treating of the various States to which they correspond. Another characteristic stream of Mexico is the River Nazas, whose waters, nearly all absorbed by the irrigation canals of the Laguna region, where the famous cotton plantations are, fall in times of flood into the Lagoon of Parras, where they evaporate, the system forming a hydrographic entity, without outlet either to the Pacific or Atlantic watershed. Thus it is seen that most Mexican rivers simply rise in and descend on one or the other slopes of the country; and as the fall is rapid their courses are interrupted by numerous cascades. Except in few cases, these rivers are of no service for navigation, but the elements of water-power and irrigation facilities which they possess are more than compensating circumstances. In addition, their scenic value is very marked in many cases.