Cuenca del Valsequillo

South of Puebla city, the Valsequillo basin brings together two stories. One is the Valsequillo reservoir, the most important in the state, which spreads across the south of Puebla municipality and its neighbours and whose canals carry irrigation water as far as the Tehuacán valley. The other is far older: the basin's sediments have yielded so many animal fossils and stone tools that it became one of the most contested places in American archaeology.

In 1962 the archaeologist Cynthia Irwin-Williams, with Juan Armenta Camacho, began digging at Hueyatlaco, a site she described as a place where animals were hunted and butchered. Scrapers, double-edged blades and other tools turned up, many of non-local stone. The dates caused the controversy: geological analyses gave conflicting estimates of 25,000 to 370,000 years, far older than any other evidence of humans in the Americas, and as early as 1967 José Luis Lorenzo of INAH claimed that some pieces had been planted. The debate has never fully closed.

In 2003 a team from Liverpool John Moores University led by Silvia González announced possible human footprints about 40,000 years old in the basin's volcanic ash; they were later shown to be quarry marks, not footprints. Besides Hueyatlaco, sites such as Cerro de Toluquilla have been excavated. Today the reservoir is a landscape of water, birds and hills a few kilometres from the city, though its water is not safe to drink.