Northern Central America took shape during uplift in the Triassic, large than its current area and extending east to the Nicaragua Rise.
[1] Much of the terrain and coastline of the country is defined by volcanoes and volcanic deposits produced from the subduction of the Cocos Plate.
[2][3] On the surface, rocks in El Salvador primarily date to the Pliocene and early Pleistocene and are typically volcanic.
Some of the oldest surface exposures are in the Metapan area, with pre-Mesozoic monzonite together with Cretaceous marine limestone, overlain by Paleogene volcanic and terrestrial sedimentary rocks.
El Salvador has extensive large vertebrate fossils from the Cenozoic, including mammoth, mastodon, megatherium, toxodont, bison, ground sloth and camelid remains.