The surface consists of a narrow coastal zone where tropical conditions prevail, a broad belt of mountainous country covered by the ranges of the Sierra Madre Occidental and their intervening valleys where oak and pine forests are to be found, and an intervening zone among the foothills of the Sierra Madre up to an elevation of 2000 ft., where the conditions are subtropical.
Near the 10th parallel the great chain again divides, the eastern part crossing the southern end of the plateau, and the western, or Sierra Madre del Sur, following the shore line closely to Tehuantepec. The Sierra Madre Occidental has but few noteworthy elevations, its culminating points being the Nevado de Colima (14,363 ft.) and Volcan de Colima (12,750 ft.) in the state of Jalisco.
Its territory is divided into two nearly equal parts by the eastern branch of the Sierra Madre Occidental, the northern part belonging to the great central plateau region, and the southern to an extremely broken region formed by the diverging branches of the Sierra Madre, with their wooded terraces and slopes and highly fertile valleys.
Nuevo Leon lies partly upon the great Mexican plateau and partly upon its eastern slopes, the Sierra Madre Oriental crossing the state N.W.
The longest is the Yaqui, which has its source on the eastern side of the Sierra Tarahumare in Chihuahua and breaks through several ranges of the Sierra Madre before reaching the gulf near Guaymas.
The surface of the state is much broken by the Sierra Madre Occidental, which extends through it from north to south and covers its entire width with parallel ranges, enclosing fertile valleys.
A few of the streams of the Pacific slope actually rise in the Altos, and force a way through the Sierra Madre at the bottom of deep ravines.
The largest rivers of Mexico are: the Rio Grande de Santiago, called the Lerma above Lake Chapala, rising in the state of Mexico and flowing westward across Guanajuato, Jalisco and Tepic to the Pacific coast, with a total length of 540 m., celebrated for its deep canyons and waterfalls; the Rio de las Balsas, or Mescala, which rises in Tlaxcala and flows south and west to the Pacific with a course of 426 m.; the Yaqui, which rises in western Chihuahua and, after breaking through the northern ranges of the Sierra Madre Occidental, flows south-westerly across Sonora to the Gulf of California, with a length of 390 m.; the Grijalva, also called the Chiapas on its upper course, which has its sources in the state of Chiapas and flows north-west and north across Tabasco to the Gulf of Mexico, with a total length of 350 m.; the Fuerte, which rises in southern Chihuahua and, after breaking through the sierras, flows south-west across Sinaloa to the Gulf of California, with a course of 340 m.; the Usumacinta, which is formed by the confluence of the Chixoy and Pasion on the east frontier of Chiapas, and flows north-west across Tabasco to the Grijalva, with a course of 330 m.; and the Panuco, which has its source in the north-west of the state of Mexico and flows north-eastward to the Gulf of Mexico.
The Sierra Madre Occidental consists of several parallel ranges in the north, where a broad belt of country is covered with a labyrinth of ridges and valleys.
They inhabit the western Sierra Madre region from Sinaloa southward to Chiapas, the higher plateau states, which region was the centre of their empire when Cortes conquered them, and parts of Vera Cruz, Tabasco, Oaxaca, Morelos, Aguascalientes and San Luis Potosi.