Mexico’s continental and peninsular area of approximately 2,000,000 km2 between 15°N and 32°30′N comprises dryclimate latitudes north of the Tropic of Cancer, so that about 60 percent of the northern part of the country is desert or semidesert. The main physiographic elements are shown on Figure 1.
The Sierra Madre Occidental and Sierra Madre del Sur are formed principally by a 2,000-m thickness of interbedded extrusive volcanic and pyroclastic rocks, apparently generated by early and mid-Tertiary volcanic emissions through extensive fissures and northwest-trending faults, and middle to late Tertiary granodioritic igneous intrusions. This volcanic sequence overlies a Precambrian metamorphic basement in portions of the states of Sonora, Oaxaca, and Chiapas. Strong fluvial and tectonic erosion has deeply carved both mountain ranges, giving rise to a large number of geohydrologically important river basins (Fig. 2).
Figures & Tables
This volume was developed, produced, and privately printed in Mexico, in Spanish, by the late Ing. G.P. Salas in 1988, as a Mexican contribution to the Geology of North America, with the understanding that it would be translated into English for inclusion in the set. The translation is by Dr. Cecily Petzall of Caracas, Venezuela, with considerable figure translation and redrafting provided by GSA. Salas worked on the volume until his death, with much valuable help from Ing. Hugo Cortez Guzmán. The result is a valuable English-language synthesis of the information available to Salas in the early to mid-1980s about the geothermal, coal, and metal-mining sectors (and some non-metallic resources) of the economic geology of Mexico.