II.

Land and Resources

Mexico extends along the entire southern border of the United States, from Tijuana, just south of San Diego, California, southeast to Matamoros, along the Gulf Coast of Texas just below Brownsville. The entire border between Texas and Mexico follows the Rio Grande. Mexico is more than 2,000 km (1,200 mi) wide along its northern border with the United States, but narrows to only 210 km (130 mi) in the south, between the Bay of Campeche and the Gulf of Tehuantepec. In northwestern Mexico, the peninsula of Baja California extends southeast below California. In the southeastern part of the country, the Yucatán Peninsula extends northeast toward Cuba, separating the Gulf of Mexico from the Caribbean Sea.

Mexico is a mountainous country with a large central plateau and relatively small amounts of naturally fertile land. Much of the country is characterized by a semiarid climate with limited rainfall. The varied topography and climate in other regions have contributed to regional diversity and uneven economic development.

The capital, Mexico City, has long served as the hub of the country’s development, and most major north-south transportation links pass through the city. Mexico’s population has historically been concentrated in the central regions of the country, with development moving northward along the central plateau. The south—characterized by dense forests, a tropical climate, a largely indigenous population, and a rural-based economy—is much less developed than the rest of the country.

Since World War II (1939-1945), the northern border states have been the focus of heavy government investment and have attracted increasing internal migration. Agricultural lands in these northern regions are often irrigated. Industrial enterprises, including border assembly industries, characterize much of this region. Due to the resources recently invested along Mexico’s northern border, as well as the proximity of the United States, northern Mexico and the border region now host some of the most economically advanced areas in Mexico.

A.

Natural Regions

Mexico can be divided into a number of main physical regions, based largely upon elevation. These include the immense central plateau, the Pacific lowlands, the Gulf Coast plains, the Yucatán Peninsula, the Southern Highlands, the Chiapas Highlands, and the Baja California Peninsula.

Mexico’s most distinguishing physical feature is the central plateau, which runs from the northern border with the United States as far south as the Isthmus of Tehuantepec. The plateau is flanked by two major mountain ranges—the Sierra Madre Occidental in the west and the Sierra Madre Oriental in the east—that fall off sharply to narrow coastal plains. These ranges come together about 240 km (about 150 mi) southeast of Mexico City. Both have historically been major barriers to transportation between the central plateau and the coastal plains.

The plateau generally ranges in elevation from about 900 m (about 3,000 ft) in the north to about 2,400 m (about 8,000 ft) in the south. Most of Mexico’s major peaks and inactive volcanoes are located on this plateau. These include Popocatépetl (5,452 m/17,887 ft) and Ixtaccíhuatl (5,286 m/17,343 ft), both of which are located near Mexico City, and the highest peak in Mexico, Pico de Orizaba (5,610 m/18,406 ft), located northwest of the Gulf Coast city of Veracruz. Many of Mexico’s major cities, including Mexico City, are located in smaller basins within the central plateau and are surrounded by mountains. The large basin where Mexico City is located has been known historically as the Valley of Mexico. As with California to the north, Mexico has frequent seismic activity, and earthquakes are fairly common in the capital city. In 1985 a major earthquake in Mexico City killed thousands and left nearly 30,000 homeless.

Between the Sierra Madre Occidental and the Pacific Ocean (including the Gulf of California) are the Pacific Coast lowlands. This western coastal plain ranges from about 50 km (about 30 mi) wide in the north to just a few kilometers wide south of Cape Corrientes, directly west of the city of Guadalajara. The plain widens again near the Isthmus of Tehuantepec in the south. The irrigated northern regions are used heavily for agricultural production.

The Gulf Coast plain, which lies between the Sierra Madre Oriental and the Gulf of Mexico, is about 280 km (about 175 mi) wide at the border with Texas. It narrows to a width of just a few kilometers near Veracruz in the south, and then widens again at the Isthmus of Tehuantepec. The coast is characterized by swampy lowlands and numerous lagoons. The northern region is generally dry, and agriculture is possible only with the help of irrigation. Rainfall is more plentiful in the south, where there are tropical forests and some fertile farmland. The country’s most important port, Veracruz, is located in this region, which is also the site of many of Mexico’s petroleum discoveries.

The Yucatán Peninsula extends northeast from the Isthmus of Tehuantepec into the Gulf of Mexico. It is a flat, low-lying region without surface rivers. The northwestern peninsula is dry and brushy and supports some agriculture; further south rainfall is plentiful and the peninsula is covered by tropical rain forests. The important international tourist center of Cancún is located along the eastern coast of the Yucatán.

The Southern Highlands, located south of the central plateau, are made up of a number of steep mountain ranges, deep valleys, and dry plateaus. The Sierra Madre del Sur range dominates this region, rising in the west near the mouth of the Balsas River. The range generally runs parallel to the Pacific coast until reaching the Gulf of Tehuantepec in the east; in many areas the mountains meet the sea, creating a rugged coastline. This scenic coastal region has become known as the Mexican Riviera and is the site of a number of coastal resort cities, including Acapulco and Puerto Vallarta. Inland valleys are hot and dry and support some irrigated agriculture.

South and east of the Isthmus of Tehuantepec, bordering Guatemala, are the Chiapas Highlands. Much of this region receives heavy rainfall and is covered by tropical forests. Some mountains in the Chiapas Highlands rise to more than 2,700 m (9,000 ft). Many of the residents of this sparsely populated area are Native Americans who work on subsistence farms or plantations.

In the far northwest of the country is the Baja California Peninsula. Stretching from the U.S. border southeast for 1,300 km (800 mi), the peninsula is extremely arid and mountainous, with a very narrow coastal plain. It is largely unpopulated, but has become increasingly attractive to U.S. tourists who visit coastal resorts along the northern Gulf of California and on the Pacific Ocean.

B.

Rivers and Lakes

Mexico’s rivers are not navigable by large ships. Rather than serving as communications or commercial links, they have been harnessed as major sources of hydroelectric power, especially since the 1950s. Dams on these rivers also serve to prevent annual flood damage.

Among the country's most important rivers is the Grijalva, which originates in Guatemala but flows through the state of Chiapas and then empties into the Gulf of Mexico near Villahermosa. It is navigable in places by small boats. Another important river is the Usumacinta, which also originates in Guatemala. The Usumacinta takes a more easterly route through Chiapas and joins the Grijalva near the Gulf of Mexico. The Infiernillo dam, on the Balsas River southwest of Mexico City, forms one of the largest reservoirs in the country and makes up much of the border between the states of Guerrero and Michoacán. The Papaloapan River originates in the mountains north of the narrow neck of the Isthmus of Tehuantepec, and empties into the Gulf of Mexico near Coatzacoalcos, which boasts another major river by the same name.

The Grande de Santiago and Lerma rivers together form the largest and most important river system in Mexico. The Lerma originates in the Sierra Madre Occidental and flows into Lake Chapala. The Grande de Santiago drains out of the lake and empties into the Pacific Ocean in the state of Nayarit. It is a significant source of hydroelectric power. The Río Bravo (known as the Rio Grande in the United States) delineates the entire Texas-Mexico border and provides water for major irrigation projects in both countries. Mexico does not have many large lakes. Lake Chapala, south of the city of Guadalajara, is the largest in the country at about 80 km (about 50 mi) long and about 13 km (about 8 mi) wide.

C.

Coastline

Mexico’s coastline totals about 9,330 km (about 5,797 mi) in length, with its western coast being about twice as long as its eastern coast. The country has few good harbors. Tampico, Veracruz, and Coatzacoalcos are major ports on the Gulf of Mexico. Important Pacific ports include Acapulco, Manzanillo, Mazatlán, and Salina Cruz.

D.

Plant and Animal Life

Much of northern Mexico is covered by desert vegetation, including mesquite, cactus, desert scrub, and some grasses. The higher regions are forested largely with hardwoods such as oak, and needle-leafed trees such as pine and fir. Expansive grasslands also cover large parts of this region. The low-lying areas of southern Mexico are typically covered by tropical rain forests that contain a great variety of trees and ferns. Much of the forests of central Mexico were destroyed before the Spanish conquest or during the colonial era. Between 1990 and 2005, deforestation continued at an average rate of 0.5 percent per year, and Mexico lost a total of 260,000 hectares (0.6 million acres) of forest.

Some of the animals found in Central and South America—such as monkeys, tapirs, and jaguars—remain in parts of southern Mexico. This is especially true in the rain forests of Chiapas and the southern Pacific coast, where human settlement is sparse and population densities have remained relatively low compared to the northern regions of the country. As a consequence, more of the natural flora and fauna have survived in southern Mexico.

The introduction of large numbers of domesticated animals in central and northern Mexico, as well as the density of human settlement, have considerably reduced the natural wildlife populations in these regions. However, bear, deer, coyote, peccary, and mountain lion remain in the rugged, mountainous regions of the Sierra Madre. Environmental groups have tried to protect Mexico’s endangered species, particularly marine turtles, from further exploitation and decline, but 57 bird species, 72 mammal species, 21 reptile species, 106 fish species, 41 invertebrates, and 190 amphibians have been deemed to be threatened in Mexico as of 2004.

E.

Natural Resources

Most of Mexico’s natural resources are below the soil. The country’s semiarid climate, its lack of rainfall, and its limited amounts of fertile land have made large-scale agriculture difficult. Only about 13 percent of Mexico’s land is cultivated. Forests cover approximately 34 percent of the nation, giving Mexico some of the world’s largest remaining forest reserves, despite the high levels of deforestation. Most of these forests are found in the Sierra Madre ranges, and in the rainy, tropical regions of the Yucatán Peninsula and the Chiapas Highlands. Mexico has large deposits of silver, copper, salt, fluorite, iron, manganese, sulfur, phosphate, zinc, tungsten, molybdenum, gold, and gypsum. Petroleum is the country’s single most valuable mineral resource. Most of the major reserves have been discovered along the Gulf Coast, either inland or in the Gulf of Mexico.

F.

Climate

The climate throughout much of Mexico is characterized by high temperatures and moderate to low rainfall. The highland climates vary considerably with elevation, but the central plateau generally has a moderate climate with few extremes of hot or cold. Mexico City, for example, has an average July high temperature of 23°C (74°F) and an average January high temperature of 21°C (70°F). Cities at lower elevations on the plateau have somewhat warmer climates. The northern and central areas of the plateau are arid and semiarid, with the drier regions receiving about 300 mm (about 12 in) of rainfall annually. Rainfall increases in the southern regions of the plateau, which receive about 500 to 650 mm (about 20 to 26 in) of rainfall annually, with most of it typically falling in the summer. Traditional rainfall patterns in the Valley of Mexico have been altered by substantial industrial pollution, which has become so serious that the rainy and dry seasons no longer follow a regular annual cycle.

Much of northwest Mexico—including Baja California and the northern regions of the Pacific Coast lowlands—is quite arid, receiving less than 130 mm (5 in) of rain per year. The northern Gulf Coast plains are semiarid, receiving about 250 to 560 mm (about 10 to 22 in) of rainfall annually. As on the central plateau, rainfall increases toward the south on both the western and eastern coasts.

The Tropic of Cancer, which marks the northern limits of the tropics, passes through the southern tip of Baja California and crosses central Mexico. Much of southern Mexico has a tropical climate with distinct rainy and dry seasons; the Gulf Coast has more regular and abundant rainfall than the southern regions of the Pacific Coast. Temperatures in these coastal regions range between 21 and 27°C (70 and 80°F) during the year. Annual rainfall, which generally ranges between 1,500 and 2,000 mm (60 and 80 in), comes mainly during the rainy season of May to October. Mexico’s Gulf Coast is subject to hurricanes that pass through the region and often cause extensive damage.

The northern Yucatán Peninsula is hot and semiarid. Annual rainfall ranges between 500 and 1,000 mm (20 and 40 in). The extreme southern part of Mexico, including the Chiapas Highlands and the southern regions of the Yucatán Peninsula, is rainy and tropical. The climate in this region is generally hot and humid, with annual average temperatures of more than 24°C (75°F). Maximum precipitation occurs in summer, with average annual rainfall exceeding 2,030 mm (80 in) in some areas.

G.

Environmental Issues

Mexicans have become increasingly aware of environmental issues, ranging from water pollution to the potential side effects of nuclear power. The development of border industries along the northern frontier with the United States has drawn attention to these issues, as these industries have contributed heavily to numerous forms of pollution that have adversely affected both sides of the border. Groups in many border communities, as well as local governments in both countries, have worked together to improve environmental conditions, particularly those related to toxic waste disposal and water pollution.

In central Mexico, the most pronounced environmental problems are the dumping of toxins into local rivers and air pollution, especially in the capital city. High levels of dangerous air pollutants in Mexico City are exacerbated by its natural setting, located in a basin surrounded by mountains. Unless it rains or sufficient breezes occur, airborne particles create a heavy smog on most days. The government has tried to reduce pollution by controlling industrial emissions and limiting the number of automobiles that can be driven daily. Mexican citizens, unsatisfied with the pace and level of government efforts, have organized grassroots environmental groups. Some have begun to support political candidates at the national level who run on green, or environmentally friendly, campaigns. Domestic and international conservation groups are working in Mexico to create biological preserves, such as the Montes Azules Biosphere Reserve in the Lacandón rain forest on the border with Guatemala.