Geology of the Southeastern Region of Mexico
For the description of the region of southeastern Mexico, the following limits have been selected: on the west, the Isthmus of Tehuantepec; to the north, the shores of the Gulf of Mexico; and to the south, the Pacific coast. The region includes the physiographic provinces of the Chiapas Mountains, the Central American Cordillera, the Yucatán Peninsula and the eastern extreme of the coastal plain of the southern Gulf (see Figure 1.1).
The climate of this region varies from temperate and semi-arid in the high parts of the Sierra de Soconusco and Sierra de Chiapas to hot in the coastal plain of the Gulf and Pacific as well as in the central depression of Chiapas. In this last area the climates are subhumid and different from the coastal plains where they are generally humid. In the Yucatán Peninsula the climate is typically hot and subhumid. In all places in southeastern Mexico the rainy season is in the summer except in some areas of the Gulf Coastal Plain where rains occur all year.
In the region that includes the states of Chiapas and Tabasco, a great sequence of Mesozoic and Cenozoic rocks crops out. It consists principally of marine sedimentary rocks that are folded and faulted.
This sequence rests discordantly on a crystalline basement of Precambrian and Paleozoic rocks that crops out to the southwest of the region, where the crystalline rocks of these Eras form an outlying metamor-phic and plutonic complex constituting the nucleus of the Sierra de Soconusco.