Sierra Madre Reaching Isthmus of Tehuantepec, Mexico17.8N 95.2W
The part of Mexico where the land is narrowest, on the right side of this image, is the Isthmus of Tehuantepec. It is located between the Gulf of Campeche (part of the Gulf of Mexico) to the north, and the Gulf of Tehuantepec (of the Pacific Ocean) to the south.
The Sierra Madre breaks down at the isthmus into a broad, plateau-like ridge. Its higher zones, however, are visible to the west in the left half of the image; their height is evident in comparison with the flat, low-lying lands along the coastline.