page_title: Valley of Mexico
section_title: Old lake system
hierarchical_section_title: Valley of Mexico / Hydrology / Old lake system
caption_attribution_description: English: Excerpt from Map Of The Valley Of Mexico and the Surrounding Mountains, by Bruff, J. Goldsborough; Disturnell, John, 1847, highlighting Lake Chalco.
context_page_description: The Valley of Mexico is a highlands plateau in central Mexico roughly coterminous with present-day Mexico City and the eastern half of the State of Mexico. Surrounded by mountains and volcanoes, the Valley of Mexico was a centre for several pre-Columbian civilizations, including Teotihuacan, the Toltec, and the Aztec. The ancient Aztec term Anahuac 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.
  The Valley of Mexico is located in the Trans-Mexican Volcanic Belt.
  The valley contains most of the Mexico City Metropolitan Area, as well as parts of the State of Mexico, Hidalgo, Tlaxcala, and Puebla. The Valley of Mexico can be subdivided into four basins, but the largest and most-studied is the area that contains Mexico City. This section of the valley in particular is colloquially referred to as the "Valley of Mexico".
  The valley has a minimum elevation of 2,200 meters above sea level and is surrounded by mountains and volcanoes that reach elevations of over 5,000 meters.
context_section_description: Before the 20th century, the Mexico City portion of the valley contained a series of lakes, with saline lakes to the north near the town of Texcoco and freshwater ones to the south. The five lakes, Zumpango, Xaltoca, Xochimilco, Chalco, and the largest, Texcoco used to cover about 1,500 km² (580 sq mi) of the basin floor. Small mountains such as the Sierra de Guadalupe and Mount Chiconaultla partially separated the lakes from each other. All the other lakes flowed toward the lower Lake Texcoco, which was saline due to evaporation. The lakes were fed by a number of rivers such as the San Joaquin, San Antonio Abad, Tacubaya, Becerra, Mixcoac and Magdalena Contreras, carrying runoff and snowmelt from the mountains.
  Long before the arrival of the Spanish, the lake system had been shrinking due to climate change. Warmer temperatures had increased evaporation and reduced rainfall in the area so that the lakes’ waters were shallow at about five meters (16 ft) deep as early as the Tlapacoya culture, around 10,000 BCE. During the Aztec Empire, the northern lakes were inaccessible by canoe during the dry season from October to May.
caption: An 1847 map of Lake Xochimilco and Lake Chalco
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