The Mezquital Valley is a series of small valleys and flat areas located in Central Mexico, about 60 kilometres north of Mexico City, located in the western part of the state of Hidalgo. It is part of the Trans-Mexican Volcanic Belt, with altitudes between 1,700 metres and 2,100 metres above sea level. It is one of Mexico's main semi-arid/area regions, whose native vegetation is dominated by cactus species, mesquite trees, and maguey with pine and oak trees in the highest elevations. It is considered to be part of the northern extension of Mesoamerica, with one major archeological site, Tula, which was the main city of the Toltecs, an important influence for the later Aztecs. However, from the Aztec period to the 20th century, it was sparsely populated and very poor, with one main indigenous ethnicity, the Otomis. In the 20th century, irrigation works were created to take advantage of the water in the Tula River, along with wastewater drained from the Valley of Mexico for agriculture. Today the valley produces various grains and produce, including one-quarter of all green chili peppers grown in Mexico.