The local basement for the volcano-sedimentary sequences is the Balsas Group (Figure 2b), which is a continental red bed sequence that is widespread in central and southern Mexico. Age of the Balsas Group ranges from Late Cretaceous
to Eocene. González et al. (2006a) summarized the stratigraphy, with older deposits in the eastern sector, east of the Barranca Calpulapan are the Zacachimalpa or Calpulapan tuffs and lake sediments and the Ixcalo lavas