Site in central Mexico on ancient Lake Chalco with human remains dated to 21,000 BC. The site has produced important archaeological information from several different periods, and environmental data from the Pleistocene onwards. There are chipped stone tools with radiocarbon dates of c 22-20,000 BC. Sedentary life occurred between 6000-4500 BC during the pre-ceramic period, and a sequence of Pre-Classic pottery styles has given information on early village life in the Basin of Mexico. The small Pre-Classic village site has an early pyramid and Olmec cultural material.