The sedimentary and volcanic sequence of southeastern Guatemala is similar to that in bordering western Honduras.
A metamorphic complex of probable Paleozoic age is overlain unconformably by red continental clastic rocks of the Late Jurassic-Early Cretaceous Todos Santos Formation, and carbonate rocks and shale of the Yojoa Group of Aptian?-Cenomanian? age. Both of these rock-stratigraphic units are relatively thick a few kilometers south of Jocotán, but only a few scattered outcrops remain north of the Jocotán-Chamelecón fault zone. The Subinal Formation, a sequence of interbedded terrestrial sedimentary and volcanic rocks, unconformably overlies the pre-Tertiary rocks. Red and olive-gray phyllarenites and calclithites are most common in the lower part of the formation. Locally, gypsum is interbedded. Rhyolitic tuff and volcanic arenite are found in the middle and upper parts. These rocks are overlain gradationally and concordantly by the Padre Miguel Group of Miocene?-Pleistocene? age, a series of basalt and felsitic ash-flow tuffs with local interbeds of volcanic arenite, tuff, and lahar.