The Campanario Formation is 15.3 to 7million years old and forms much of the basement in the Laguna del Maule area; this geological formation contains andesitic-dacitic ignimbrites and tuffs with later dacitic dykes that were emplaced 3.6-2.0 million years ago. An older unit, of Jurassic-Cretaceous age, crops out northwest of the volcanic field. Other units include an Oligocene-Miocene group of lacustrine and fluvial formations named Cura-Mallín, and another intermediary formation named Trapa-Trapa which is of volcanic origin and between 19and 10million years old. Remnants of Quaternary ignimbrites and Pliocene, early Quaternary volcanic centres, are also found around the field; they form the Cola del Zorro Formation which is partly covered by the eruption products of Laguna del Maule.