Mexico has a varied topography consisting mainly of plateaus in the eastern two-thirds of the national territory and a mountainous spine running through the western third of the country. The interior north of the Mexico City metropolitan area is mainly high plateau-known as the Mesa Central and Mesa del Norte. The average elevation in the plateaus ranges from about 900 meters in the north to 2,400 meters in the southern portion of the Mesa Central. In the far northwest, the Baja Peninsula stretches southeast from the U.S. border for 1,300 kilometers. The peninsula is extremely dry and rugged, with a very narrow coastal plain. The southern highlands, located south of the Mesa Central, contain a number of steep mountain ranges, deep valleys, and dry plateaus. The Yucatan Peninsula extends northeast from the Isthmus of Tehuantepec into the Gulf of Mexico. It is a flat, low-lying limestone plateau lacking in major rivers.
Rising rapidly by a succession of terraces from the low sandy coast on the east and west, Mexico culminates in a central plateau running in a northwesterly and southeasterly direction, and having an elevation varying from 4,000 to 8,000 feet (1,219 to 2,438 meters) above the sea. It is preeminently a region of mountain elevations; but this is not always to be recognized in the interior on account of the development of it's broad table-land, whose flat or gently undulating surface, rising from the depression of the Rio Grande to graduated altitudes, masks the configuration of the land.
Much of this plateau has been formed through a progressive and long-continued accumulation of detrital material, representing in part the distributed products resulting from mountain destruction, and in greater part the discharges from an almost endless number of volcanic openings. These have filled the original valleys to the lips, and it is thus upon a new surface that the more recent or existing valleys have been imposed. Thus the great central plateau appears to be merely a filled-up series of troughs, through whose margins alone the buried mountains protrude their summit peaks. In Mexico, too, especially in the loftier parts of the plateau, buried mountains rear their summits as "islands" above the enveloping mass; elsewhere they make continuous ridges or chains, whose crest lines may be as much as 10,000 feet (3,048 meters) above the sea.
The eastern coast of Mexico, bathed by the Caribbean Sea and the Gulf of Mexico, is flat, low, and sandy, except in a few places where the mountains are so close as to be visible from the shore. On the Pacific side the coast, though generally low, is here and there broken by spurs extending from the cordilleras to the ocean.
The principal gulfs are those of California, Tehuantepec, and Mexico. There are innumerable bays, the principal ones being Campeche on the Gulf of Mexico and Tehuantepec on the Pacific, on opposite sides of the Isthmus of Tehuantepec. The more important bays on the Gulf of California and on the seacoasts of the Republic will be mentioned in the description of the individual States. Mexico has many islands near the coasts, none of them very large and some of them uninhabited, although, as a rule, they are of great fertility and capable of supporting a large population. Among the best known are San Juan de Ulua, opposite the port of Vera Cruz, and Tiburon, off the coast of Sonora.
Two cordilleras, or high mountain ranges, traverse Mexico, running almost parallel to the coast, one along the Gulf of Mexico and the other along the Pacific. The former is from 10 to 100 miles (16 to 160 kilometers) inland, leaving an inclined plane between the sea and the foot of the mountains, while the latter is near the coast, with only a narrow strip of land between the mountains and the sea; this range has several branches running in different directions, the most continuous being the Sierra Madre of the Pacific. Parallel to this last-named range is the Sierra de la Giganta in Lower California, which slopes abruptly toward the east like the Atlantic escarpments. Corresponding with the Sierra Madre on the west are the broken eastern elevations of the central plateau.
Lesser ranges include the Sierra Madre de Chiapas and the Cordillera Neovolcánica-an east-to-west volcanic range spanning the breadth of the country just south of Mexico City. The country's highest point, the Pico de Orizaba (5,636 meters), is located within the Cordillera Neovolcánica about 193 kilometers southeast of Mexico City. Mexico has extensive lowlands largely along the Gulf coast and in the Yucatan Peninsula.
Mexico is deficient in large permanent streams, and its rivers offer but little opportunity to navigation. The topographical conditions of the country are such as to cause the streams, in their progress toward the sea, to be continually precipitated in the form of cascades, etc., thus rendering navigation difficult, but greatly facilitating their availability for motive power.
Mexico has nearly 150 rivers, two-thirds of which empty into the Pacific Ocean and the remainder into the Gulf of Mexico or the Caribbean Sea. Most rivers are short and non-navigable, running from coastal mountain ranges to the coast. Water volume is unevenly distributed throughout the country. Five rivers-the Usumacinta, Grijalva, Papaloapán, Coatzacoalcos, and Pánuco-account for 52 percent of the average annual surface water volume. Most of the larger rivers are located in the southeastern part of the country and flow into the Gulf of Mexico. Northern Mexico contains less than 10 percent of the country's water resources. The Río Bravo del Norte (known as the Rio Grande in the United States) defines Mexico's northern border from Ciudad Juárez east to the Gulf of Mexico.
Mexico has abundant natural resources. In addition to extensive subsoil resources (including large reserves of oil and silver), the country has a rich biodiversity and varied wildlife. As of 2003, about 5 percent of Mexico's land area was under a protected status. Protected sites included six wetlands of international importance (Ramsar sites) totaling 1.1 million hectares and 12 biosphere reserves totaling 6.8 million hectares.
Although nearly half of Mexico's total land area is officially classified as agricultural, only 12 percent of the total area is cultivated. Extensive irrigation projects carried out in the 1940s and 1950s greatly expanded Mexico's cropland, especially in the north. One-third of Mexican territory is officially designated as grazing land. These lands are located mainly in the north. Some 9 percent of Mexico's territory consists of forest or woodland, 59 percent of which is in the tropics, 15 percent in the subtropical zone, and 26 percent in the temperate and cool zones. Temperate forests cover some 49 million hectares, almost one-third of which are open to logging, mainly in the states of Chihuahua, Durango, and Michoacán.
The boundary with Belize (British Honduras) as fixed by the treaty of July 8, 1893, begins in the Boca de Bacalar Chica, the strait separating Yucatan 1 from the Ambergris Key, runs in the center of that channel in a southwestern direction to parallel 18° 9' north latitude, thence northwest * * * to parallel 18° 10' north.
The boundary with the Republic of Guatemala, as fixed by the treaty of September 27, 1882, and the agreement of April 1, 1895, runs from a point in the Pacific Ocean 3 leagues from the mouth of the Suchiate River, up the deepest channel of that river, to the place at which it intersects the vertical plane through the highest point of the volcano of Taeana, 25 meters (82 feet) from the southernmost garita of Talquian—this last to remain in Guatemalan territory; thence to a determined point 4 kilometers (2.48 miles) beyond the Cerro de Ixbul; thence eastward along the parallel of latitude through that point to the deepest channel of the Chixoy River; thence along this channel to the Usumacinta River, along that river to a point on the parallel 17° 49', technically described by the treaty, and finally eastward to the line of British Honduras.
The boundary with the United States, as fixed by the treaties of February 2, 1848, and December 30, 1853, begins at the mouth of the Rio Grande on the Gulf of Mexico and follows the river to El Paso, Tex. (parallel 31° 47' north). The distance along the axis of the river is 860 miles (1,384 kilometers), not counting sinuosities, which are constantly changing; the actual length of the channel is about 1,300 miles (2,092 kilometers). The total distance from El Paso to the Pacific Ocean 693 miles (1,115 kilometers), and from the Gulf of Mexico to the Pacific Ocean 1,553 miles (2,499 kilometers) if measured on the axis of the Rio Grande alone, or about 1,993 miles (3,207 kilometers) if the sinuosities of that river are considered.
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