In the Tulancingo Valley, some of the oldest human remains of Mexico were found in Tecolote Cave. However, the most important site is Huapalcalco. This site is located about three km from the center of modern Tulancingo and contains a pre-Hispanic pyramid and cave paintings. In the cliffs of Huapalcalco and nearby, there are fifty groups of cave paintings, some of which date back as far as 10,000 BCE. The pre-Hispanic site was first excavated in the 1950s by Instituto Nacional de Antropologia e Historia (INAH). Carbon dating has placed objects as far back as 1,100 BCE. In the 7th century, a ruler by the name of Quetzalcoatl ruled here until he left to found Teotihuacan. While the remains of this site do not look impressive, they are the forerunners of the Teotihuacan civilization. The center of the site is a five-level pyramid measuring twelve meters at its base and is eight meters high. The function of this site was that of a ceremonial center. At the top of the pyramid, there is a monolithic altar, which was probably used for the deposit of offerings. The name means House of Green Wood.