Together with Nicaragua and El Salvador it is underlain by the Chortis Block continental fragment.
[1] Early tectonic research in 1977 suggested a possible origin for the underlying land in the Pacific Ocean rather than on the Caribbean Plate.
Throughout the rest of the Paleogene, they became unconformably overlain by andesite lava, sedimentary rocks and rhyolite ignimbrite.
In places such as the Plantares geothermal area in the Departamento de Copan, rainwater heats up in complex faults surrounding a graben formed in these rocks.
An extensive mapping project with keys in English was conducted by the University of Texas-Austin in the early 1970s.