<P> The Sierra Madre Oriental mountain range starts at the Big Bend region of the border with the U.S. state of Texas and continues 1,350 kilometres (840 mi) until reaching Cofre de Perote, one of the major peaks of the Cordillera Neovolcánica . As is the case with the Sierra Madre Occidental, the Sierra Madre Oriental comes progressively closer to the coastline as it approaches its southern terminus, reaching to within 75 kilometres (47 mi) of the Gulf of Mexico . The northeast coastal plain extends from the eastern slope of the Sierra Madre Oriental to the Gulf of Mexico . The median elevation of the Sierra Madre Oriental is 2,200 metres (7,200 ft), with some peaks at 3,000 metres (9,800 ft). </P> <P> The Mexican Altiplano, stretching from the United States border to the Cordillera Neovolcánica, occupies the vast expanse of land between the eastern and western sierra madres . A low east - west range divides the altiplano into northern and southern sections . These two sections, previously called the Mesa del Norte and Mesa Central, are now regarded by geographers as sections of one altiplano . The northern altiplano averages 1,100 meters in elevation and continues south from the Río Bravo del Norte through the states of Zacatecas and San Luis Potosí . Various narrow, isolated ridges cross the plateaus of the northern altiplano . Numerous depressions dot the region, the largest of which is the Bolsón de Mapimí . The southern Altiplano is higher than its northern counterpart, averaging 2,000 metres (6,600 ft) in elevation . The southern altiplano contains numerous valleys originally formed by ancient lakes . Several of Mexico's most prominent cities, including Mexico City and Guadalajara, are located in the valleys of the southern Altiplano . </P> <P> One other significant mountain range, the Peninsular Ranges, cuts across the landscape of the northern half of Mexico . A southern extension of the California coastal ranges that parallel California's coast, the Mexican portion of the Peninsular Ranges extends from the United States border to the southern tip of the Baja California Peninsula, a distance of 1,430 kilometres (890 mi). Peaks in the California system range in altitude from 2,200 metres (7,200 ft) in the north to only 250 metres (820 ft) near La Paz in the south . Narrow lowlands are found on the Pacific Ocean and the Gulf of California sides of the mountains. The Cordillera Neovolcánica is a belt 900 kilometres (560 mi) long and 130 kilometres (81 mi) wide, extending from the Pacific Ocean to the Gulf of Mexico . The Cordillera Neovolcánica begins at the Río Grande de Santiago and continues south to Colima, where it turns east along the nineteenth parallel to the central portion of the state of Veracruz . The region is distinguished by considerable seismic activity and contains Mexico's highest volcanic peaks . This range contains three peaks exceeding 5,000 metres (16,000 ft): Pico de Orizaba (Citlaltépetl)--the third highest mountain in North America--and Popocatépetl and Iztaccíhuatl near Mexico City . The Cordillera Neovolcánica is regarded as the geological dividing line between North America and Central America . </P> <P> Several important mountain ranges dominate the landscape of southern and southeastern Mexico . The Sierra Madre del Sur extends 1,200 kilometers along Mexico's southern coast from the southwestern part of the Cordillera Neovolcánica to the nearly flat isthmus of Tehuantepec . Mountains in this range average 2,000 meters in elevation . The range averages 100 kilometers wide, but widens to 150 kilometers in the state of Oaxaca . The narrow southwest coastal plain extends from the Sierra Madre del Sur to the Pacific Ocean . The Sierra Madre de Oaxaca begins at Pico de Orizaba and extends in a southeasterly direction for 300 kilometers until reaching the isthmus of Tehuantepec . Peaks in the Sierra Madre de Oaxaca average 2,500 meters in elevation, with some peaks exceeding 3,000 meters . South of the isthmus of Tehuantepec, the Sierra Madre de Chiapas runs 280 kilometers along the Pacific Coast from the Oaxaca - Chiapas border to Mexico's border with Guatemala . Although average elevation is only 1,500 meters, one peak--Volcán de Tacuma--exceeds 4,000 meters in elevation . Finally, the Meseta Central de Chiapas extends 250 kilometers through the central part of Chiapas to Guatemala . The average height of peaks of the Meseta Central de Chiapas is 2,000 meters . The Chiapas central valley separates the Meseta Central de Chiapas and the Sierra Madre de Chiapas . </P>

What are the two chains of mountains that run almost the entire length of mexico