Sollipulli volcano developed on a basement which consists of the Jurassic-Cretaceous Nacientes del Biobío formation and the Pliocene-Pleistocene Nevados de Sollipulli volcanics, with subordinate exposures of the Miocene Curamallín and the Cretaceous-Tertiary Vizcacha-Cumilao complex volcano-sedimentary formations. Miocene granites are intruded into the basement.