Valley of Mexico - Hydrology

Hydrology

The Valley of Mexico is a closed basin which geologically divides into three hydrologic zones, the low plain, which is essentially the bed of now-extinct lakes, the piedmont area and the surrounding mountains. The old lakebeds correspond to the lowest elevations of the valley in the south are mostly clay with a high water content and are almost entirely covered by urban development. In the piedmont area, these clays become mixed with silts and sands, and in some areas close to the mountains, the piedmont is largely composed of basalt from old lava flows. The valley is enclosed completely by mountain ranges, from which flow rain and melting snow into the valley's hydraulic system. This groundwater flow produces a number of springs in the foothills and upwellings in the valley floor. This underground flow is the source of the five aquifers that provide much of the drinking water to Mexico City located in Soltepec, Apan, Texcoco, Chalco-Amecameca and underneath Mexico City itself.