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