,000 feet (2,400 meters) south of Mexico City. Throughout the plateau, somewhat flat basins are interrupted by mountainous outcrops.The plateau can be subdivided into two major sections. The Mesa del Norte begins near the international border and ends around San Luis Potosi. In this arid lower part of the plateau, interior drainage predominates with few permanent streams. On its west side the mesa is flanked by the largely volcanic Sierra Madre Occidental, with an average height of 8,000 to 9,000 feet (2,400 to 2,700 meters). It has been highly dissected by westward-flowing streams that eroded a series of deep barrancas, or canyons. The most spectacular of these is the Barranca del Cobre, Mexico's equivalent of the Grand Canyon. The Sierra Madre Oriental, a range of folded mountains formed of shale and limestone, is on the east side of the mesa. With average elevations similar to those of the Sierra Madre Occidental, these dissected highlands have peaks that reach 13,000 feet (4,000 meters).The Mesa Central stretches from San Luis Potosi to the volcanic axis south of Mexico City. Formed largely by volcanic action, the general plateau surface of this mesa is higher, moister, and generally flatter than the Mesa del Norte. The Mesa Central is divided into a series of fairly flat intermountain basins separated by eroded volcanic peaks. These basins are generally quite fertile and have been the most densely populated portions of Mexico for several hundred years. The largest valleys--such as those of Mexico City, Puebla, and Guadalajara--rarely exceed 100 square miles (260 square kilometers) in area, while many others are quite small. The traditional breadbasket of the country, the Bajio of Guanajuato, is located in the northern part of the mesa. Many of the basins were sites of major lakes, like those formerly located around Mexico City that were drained to facilitate European settlement. The weak, structurally unstable soils that remain hav...
