As you continue, the coastal plain gradually broadens as the Sierra shrinks to mere foothills at the Isthmus of Tehuántepec, the neck of land where Mexico (and indeed the entire North American continent) shrivels to a scant 125 miles (200 km) in width. East beyond the Isthmus, in the remote region Oaxacans call the Chimalapa, you spot a new range of mountains, the Sierra Atravesada, rising and stretching east into the neighboring state of Chiapas. The Atravesadas’ isolated rugged summits, sylvan forests, and deep gorges shelter one of Mexico’s last remaining troves of endangered plants, birds, mammals, and reptiles.

From the Isthmus, other Oaxaca regions beckon. Turning around to the left and heading your airship northwest, you follow the valley of the Río Tehuántepec, passing over the bustling, tradition-rich small cities of Juchitán and Tehuántepec and their luxuriant hinterlands of fruit, corn, and cotton. Soon, on your right toward the north, rises the grand Sierra Madre de Oaxaca. You see a succession of peaks stretching west a hundred miles, from the rugged homeland of the indigenous Mixe (MEE-shay) people in Oaxaca’s northeast to the equally mountainous domain of their neighbors, the Sierra Zapotec at the northern center of the state.

Drawn by what you might find beyond the mountain crest, you navigate your airship due north, over the Mixe country, above the gigantic spreading massif of Zempoaltepetl (only 9,000 feet/2,700 meters, but composed nevertheless of a dozen separate peaks), the Mixes’ holy mountain. Beyond that, the mountains gradually drop to foothills, where you see a great river-laced plain of tropical forest checkered with pasture, farms, and small towns, stretching north past Oaxaca’s northern lowland border with the state of Veracruz all the way to the Gulf of Mexico. The Oaxaca portion, known as the Papaloapan (pah-pah-loh-AH-pahn) for the great river system that drains it, encompasses the Chinantla and the Mazateca, homelands of the indigenous Chinantec and Mazatec peoples.