The off-shore volcanic ridges extend from Tres Vírgenes–Aguajito–La Reforma towards sea-floor spreading centers in the Guayamas basin.

It is a part of a volcanic ridge that extends from the eastern coast of Baja California towards active sea floor spreading in the Guaymas basin.

Above this intrusive rock layer is a volcanic cover from the late Cenozoic era that includes andesite from the Santa Lucía Range, and Esperanza basalt.

The Santa Rosalia Formation is beneath this volcanic cover which consists of shallow-water marine deposits identified by fossiliferous sandstone.

Above all these layers, the region consists of a variety of pyroclastic particles from different stages of its most recent volcanic activity.

These rocks produced at Las Tres Vírgenes volcanic region have characteristics like those of the calc–alkaline magma series.

[5] This complex of three stratovolcanoes began as mostly dacitic lava flows and domes which resulted in the formation of El Viejo (300 Ka).

Three of these cones are on the southern flank of El Azufre and they have elongated and coalesced shapes and are crudely aligned in N-S direction.

These scoria cones consist of massive grain supported poorly sorted fallout beds.

The Mezquital dacite lava dome is made up of two and they are located on the southern apron of the Virgen volcano.