Commercial quantities of gas have been produced from several Miocene conglomerates in the southwestern part of the Veracruz basin. These conglomerates, with their associated sandstones and shales, make up a zone 1,000 m thick, all of which was deposited in a bathyal environment.

The conglomerates consist of recycled Upper Cretaceous limestone clastic rocks containing minor amounts of igneous and metamorphic rock fragments. The clastic material was derived from the west, where a very thick section of carbonate and terrigenous rocks, Jurassic to Paleocene in age, was uplifted, folded, and thrust faulted during the Laramide orogeny. Erosion of the deformed source materials is indicated by two significant unconformities. One unconformity truncates sedimentary rocks from the Paleocene to the Upper Cretaceous, whereas the other is at the base of the Miocene. Most of the conglomerate beds are in the lower Miocene. A reconstruction of the pre-lower Miocene erosional surface serves to locate paleodrainage patterns and the areas of debouchment of deep-water fanglomerat s.

Sediments derived from the source area west of Veracruz basin were transported in a general northeasterly direction by fluvial currents which fed into deep submarine canyons. Through these canyons most of the coarse clastic sediments were carried down to the basin floor and deposited as a series of prograding submarine fans.