Geology of the Central Region of Mexico
In describing the geology of the central area of Mexico, the following limits have been used: to the north, the northern edge of the Neovolcanic axis; to the west and south, the coastlines of the Pacific; and to the east, the shore of the Gulf of Mexico and the Isthmus of Tehuantepec.
The physiographic provinces of the Neovolcanic axis, the Sierra Madre del Sur, and the northern part of the Southern Gulf Coastal Plain are included in this region (see Figure 1.1). In terms of the division of geological provinces used by López-Ramos (1979), the provinces of the Veracruz basin (with the subprovince of Sierra de Juárez), the province of San Andres Tuxtla, the Tlaxiaco basin, the Sierra Madre del Sur, the Altiplano of Oaxaca, the Guerrero-Morelos basin, and the Neovolcanic axis are included.
The climate of the region is highly variable owing to the complex physiography. On the slopes of the Gulf of Mexico the climate changes from humid temperate in high parts of the Sierra Madre Oriental, to semi-hot and humid in the lowlands. On the Pacific slopes the climates vary from hot and subhumid on the southeast flank of the Sierra Madre del Sur and the banks of the Río Balsas to semi-arid, hot, and very hot in the Valley of Oaxaca and the major part of the Balsas basin. In the regions of basins within the Neovolcanic axis, the climate is in general subhumid and varies from temperate to semi-frigid and cold.
In the central Mexico