Cerro Xico

Cerro Xico, or the Xico volcano, is a nearly perfect circular crater that rises about 100 metres above the floor of the former Lake Chalco, at 2,240 m above sea level, in the southeast of Valle de Chalco Solidaridad. The crater is roughly 1,400 metres across. It is not a cone but a tuff ring: it formed when rising magma met lake water and blew apart, an eruption Wikipedia dates to over 100,000 years ago (another passage in the same article says 550 to 640 CE, so the figures do not agree). It belongs to the Chichinautzin volcanic field.

The name comes from Nahuatl and is tied to the word for navel, and the place was long seen as the centre of the world. Digs in 1990 turned up ceremonial structures with sea shells, green stones and shell ornaments, offerings linked to water worship. After the conquest the crater dried out. Today families live on the slopes and farm inside the crater, where volcanic soil holds moisture, and people use it for walking, running and cycling.

On the ground it is hard to make out the ring's shape; it reads far better from aerial images. To round out a visit, the Museo Comunitario del Valle de Xico, in an old hacienda and open since 1996, keeps archaeological and fossil pieces from the area.