Geology of the Northwest Region of Mexico
For the description of northwestern Mexico the following natural limits have been selected in this work: to the east, the volcanic sequence of the Western Sierra Madre; to the west, the Pacific coasts of Baja California and Sinaloa; and to the south, the northern edge of the Neovolcanic axis.
In accordance with the physiographic division of the General Department of Geography (see Figure 1.1), the provinces of Baja California, the Sonoran Desert, Sierra Madre Occidental, and the Pacific Coastal Plain are included within this region. The climate varies in general from dry in Baja California, Sonora, and northern Sinaloa, to subhumid in the higher parts of the Sierra Madre Occidental and south of Mazatlán. In almost all the region rainfall comes in the summer, except in the north of Baja California where the rain is in winter.
The peninsula of Baja California as shown on the geologic map at 1:1,000,000 scale (General Department of Geography, DGG) offers a high structural complexity and rocky outcrops, which make it difficult to reconstruct a stratigraphic column for this region and to ascertain events that have occurred. Nevertheless a subdivision has been made, as rational as possible, that permits explanation, with a certain clarity, of the geologic concepts of this province and that coincides in large part with the physiographic divisions of the DGG and with the division into the geologic provinces of Lopez-Ramos (1979).
In this zone exposures of a stratigraphic sequence whose geochronologic range varies from Paleozoic to Recent are encountered. The
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Available knowledge concerning the origin and geologic structure of mexico is still incomplete. Each day scientific discoveries, advances in mapping, and new techniques of exploration offer more information toward the development of tour understanding. Nevertheless, it is still difficult to achieve a complete description of the geologic character of the territory of the nation, as well as to work out functional models to explain the origin of its geologic structure. Along with the development of geologic studies that science has made in mexico, there have been a few attempts to formulate general works covering the many aspects of geology that the country presents. Nevertheless, one must recognize that the lack of information about certain periods in the geological history of the national territory, and the numerous unexplored areas, have constituted some principal obstacles toward achieving a finished work of this type.
Inreviewing past information, it is worth indicating that in 1896 a somewhat unsettled entitled A Sketch of the Geology of Mexico formulated by Jose Guadalupe Aguilera and Ezequiel Ordonez of the Geologic Institute of Mexico, a descriptive work that constituted an important complement to and summary for the Geologic Map of Mexico, which had benn published earlier. Nevertheless, it was not until 1949 that V. Garfias and T.C. Chapin published the work entitled Geology of Mexico, in during the geological history of the republic are included.
A more recent work is The Geology of Mexico, whose author was Ing. Manuel Alvarez, Jr., and which the Faculty of Engineering of UNAM printed as notes