Most of Mexico is highland or mountainous and less than 15% of the land is arable; about 25% of the country is forested. Most of the Yucatán peninsula and the Isthmus of Tehuantepec in the southeast is lowland, and there are low-lying strips of land along the Gulf of Mexico, the Pacific Ocean, and the Gulf of California (which separates the Baja, or Lower, California peninsula from the rest of the country).
The heart of Mexico is made up of the Mexican Plateau (c.700 mi/1,130 km long and c.4,000–8,000 ft/1,220–2,440 m high), which is broken by mountain ranges and segmented by deep rifts. The plateau is fringed by two mountain ranges, the Sierra Madre Oriental (in the east) and the Sierra Madre Occidental (in the west), which converge just south of the plateau. Within the plateau are drainage basins, which have no outlet to the sea and which contain some of the country's major cities. The Laguna District, one of the drainage basins, was (1936) the scene of a major experiment in land reapportionment. In the north the plateau is arid except for irrigated areas and is used principally for raising livestock.
In the south the deserts yield to the broad, shallow lakes of a region, comprising the Valley of Mexico, known as the Anáhuac and famous for its rich cultural heritage. South of the Anáhuac, which includes Mexico City, is a chain of extinct volcanoes, including Citlaltépetl, or Orizaba (18,700 ft/5,700 m, the highest point in Mexico), Popocatépetl, and Iztaccíhuatl. To the south are jumbled masses of mountains and the Sierra Madre del Sur.
Among Mexico's few large rivers are the Rio Bravo del Norte, which forms the boundary with Texas, and its tributaries the Río Conchos and the Río Sabinas; the Río Yaqui, Río Fuerte, Río Mezquital, Río Grande de Santiago, and Río Balsas, which flow into the Pacific; and the Río Grijalva and Río Usumacinta, which flow into the Bay of Campeche. The climate of the country varies with the altitude, so that there are hot, temperate, and cool regions— tierra caliente (up to c.3,000 ft/1,220 m), tierra templada (c.3,000–c.6,000 ft/1,220–1,830 m), and tierra friá (above c.6,000 ft/1,830 m).
Mexico's 31 states are Aguascalientes, Baja California, Baja California Sur, Campeche, Chiapas, Chihuahua, Coahuila, Colima, Durango, Guanajuato, Guerrero, Hidalgo, Jalisco, Mexico, Michoacán, Morelos, Nayarit, Nuevo León, Oaxaca, Puebla, Querétaro de Arteaga, Quintana Roo, San Luis Potosí, Sinaloa, Sonora, Tabasco, Tamaulipas, Tlaxcala, Veracruz, Yucatán, and Zacatecas.
About 60% of the population are of mixed Spanish and indigenous descent, while about 30% are of purely indigenous ancestry, and 10% are of European descent. Spanish is the official language and various Mayan dialects, Nahuatl, and other indigenous languages are also spoken. Since 1920 the population of Mexico has had a very high rate of growth, almost entirely the result of natural increase; from 1940 to 2005 the population grew from less than 20 million to more than 100 million. However, declining fertility rates (from 7 children per woman in 1965 to slightly under 3 in 1998) are slowing population growth. More than 75% of the people are Roman Catholic and 6% are Protestant, but nearly 14% did not specify their religion in the census and the growing Protestant minority is believed to be much larger. The country has numerous universities, notably in Mexico City, Saltillo, Guadalajara, Monterrey, and Puebla. Since precolonial times Mexican architects, painters, writers, and musicians have produced a rich cultural heritage (see Spanish colonial art and architecture, Mexican art and architecture, and Spanish American literature).