ABSTRACT
The semi-arid zones of Mexico extend in a discontinuous form over approximately 580,000 km2 of the country's surface. Mexico also has many smaller semi-arid zones. The semi-arid zone of Sonora penetrates into the country more or less in the center north of the state and continues over the western spurs of the Sierra Madre Occidental. The semi-arid zone that borders on the Chihuahuan Desert, being the largest in the country, presents the most complicated physiography. The geological substratum of the Chihuahuan semi-arid zone is extraordinarily varied: it is possible to find deposits from the superior Paleozoic to Paleozoic: igneous, metamorphic and sedimentary. The semi-arid zones of Guerrero and Oaxaca occupy areas on bedrock, classified in principle as "Paleozoic Metamorphic" in contact with "sediments of the Cenozoic", which actually does not mean anything. The range of meteorological conditions that characterizes the Mexican semi-arid zones is mainly determined by the altitude and the latitude, which act irregularly, favoring the variety of climates.
