The general slope of the southern part is southward to the river Balsas, or Mescala, which forms its boundary-line with Guerrero.
Chilpancingo, in Guerrero, was badly shattered in 1902, and in 1907, and in 1909 was reduced to a mass of ruins.
Similar rocks occur also in Chiapas, Oaxaca, Guerrero and elsewhere; but owing to the absence of any early fossiliferous deposits, the age of these rocks is very uncertain.
The tierra templada, or sub-tropical zone, rises to an elevation of 5577 ft., and comprises " the greater portions of Coahuila, Nuevo Leon, San Luis Potosi, nearly half of Tamaulipas, a small part of Vera Cruz, nearly the whole of Chiapas, nearly all of Oaxaca, a large portion of Guerrero, Jalisco, Sinaloa and Sonora," together with small parts of the inland states of Puebla, Mexico, Morelos and Michoacan.
The Mistecas, or Mixtecas, and Zapotecas, who occupy the southern slopes of the central plateau, especially Puebla, Morelos, Oaxaca and Guerrero, form another distinct race, whose traditional history goes back to the period when the structures now known as Mitla, Monte Alban, Xochicalco and Zaachila were built.