Isthmus of Tehuantepec - Geography

Geography

The isthmus includes the part of Mexico lying between the 94th and 96th meridians west longitude, or the southeastern parts of Veracruz and Oaxaca, including small areas of Chiapas and Tabasco. The states of Tabasco and Chiapas are east of the isthmus, with Veracruz and Oaxaca on the west.

At its narrowest point, the isthmus is 200 km (120 mi) across from gulf to gulf, or 192 km (119 mi) to the head of Laguna Superior on the Pacific coast. The Sierra Madre breaks down at this point into a broad, plateau-like ridge, whose elevation, at the highest point reached by the Ferrocarril Transistmico railway at Chivela Pass, is 224 m (735 ft). The northern side of the isthmus is swampy and densely covered with jungle, which has been a greater obstacle to railway construction than the grades in crossing the sierra. The Selva Zoque in the eastern-central region of the isthmus is an area of great ecological importance, the largest remaining area of tropical rainforest in Mexico with the majority of the terrestrial biodiversity in Mexico.

The Sierra Madre de Oaxaca mountains flatten out to form Chivela Pass before the Sierra Madre de Chiapas mountains resume to the south, so geographically the isthmus divides North America from Central America. However, the southern edge of the North American tectonic plate lies across the Motagua Fault in Guatemala, so geologically, the division between North America and Central America (on the Caribbean Plate) is much farther south than the isthmus of Tehuantepec.