Transect H-3 extends 460 krn across southern Mexico from the Pacific Ocean to the Gulf of Mexico, far south of cratonic North America. The transect has two segments: one trending N7°E from the axis of the Acapulco Trench to central Oaxaca and another extending N53°W from central Oaxaca to the Gulf of Mexico. The cross sections lie near the middle of the transect and coincide with a line connecting Puerto Escondido at the Pacific coast, the city of Oaxaca, and San Martin Tuxtlas Volcano near the NE end of the transect

The mosaic of geologic provinces along the corridor made it convenient to use a tectonostratigraphic approach for the analysis of the geologic history. Terrane nomenclature in this report is derived from names of pre-Hispanic cultures dominant in each respective region. The geologic description of terranes and the bases of their discrimination are given below.