Mexico: Valley of Mexico. Anahuac Valley.

A NASA satellite image of smog in the Valley of Mexico in 1985

Anahuac_Valley 
http://en.wikipedia.org/wiki/Anahuac_Valley

The Valley of Mexico is a highlands plateau in central Mexico roughly coterminous with the present-day Distrito Federal and the eastern half of the State of Mexico. Surrounded by mountains and volcanoes, the Valley of Mexico was a centre for several pre-Columbiancivilizations, including Teotihuacan, the Toltec, and the Aztec. The ancient Aztec termAnahuac (Land Between the Waters) and the phrase Basin of Mexico are both used at times to refer to the Valley of Mexico. The Basin of Mexico became a well known site that epitomized the scene of early Classic Mesoamerican cultural development as well.