Mexico, officially United Mexican States, republic (1995 est. pop. 93,986,000), 761,600 sq mi (1,972,544 sq km), S North America; bordered by the U.S. (N), the Gulf of Mexico and the Caribbean Sea (E), Belize and Guatemala (SE), and the Pacific Ocean (W). Principal cities include Mexico City (the capital), Guadalajara, and Monterrey. The country is predominantly mountainous, and less than 15% of the land is considered arable. There are lowlands in the southeast and along the coasts, but the heart of the country is the extensive Mexican plateau, with elevations generally above 4,000 ft (1,220 m). Fringed by the ranges of the Sierra Madre, the plateau (except for the arid north) is a region of broad, shallow lakes where more than half of the country's population is concentrated. To the south is a chain of extinct volcanoes, including Popocatepetl, Ixtacihuatl, and Citlaltepetl, which at 18,406 ft (5,610 m) is Mexico's highest point. Since World War II Mexico has had considerable economic growth. Agriculture engages about a quarter of the active workforce and is slowly being modernized. Major irrigation projects have increased yields. Cotton, coffee, sugar, and tomatoes are the major export crops, and much corn, wheat, beans, and citrus fruits are grown. Livestock raising and fishing are also significant. Mexico has considerable mineral resources, including vast petroleum reserves and zinc, sulfur, silver, antimony, copper, and manganese. Industries, usually in or near the larger cities, produce iron and steel, motor vehicles, engines, processed foods, refined petroleum and petrochemicals, chemical fertilizers, and other products. Assembly factories (maquiladoras) along the U.S. border are a major source of foreign income. Tourism is also economically important. The population has grown rapidly in the 20th cent., more than quadrupling from 1940 to 1990. However, declining fertility rates are slowing population growth. The great majority of the people are of mixed Spanish and indigenous descent, but a sizable minority are of purely indigenous descent. The official language is Spanish, but some Mexicans still speak only indigenous tongues. About 90% of the people are Roman Catholic.