Volcanism in the southern Puna region initiated about 8 million years ago and took place in several stages, which were characterized by the emplacement of lava domes and of ignimbrites such as the 4.0 - 3.7 million years old Laguna Amarga-Laguna Verde ignimbrites. Some of the domes are located close to the border with Chile in the Ojos del Salado and Nevado Tres Cruces area. Later there also were mafic eruptions, which generated lava flows in the Carachipampa and Laguna de Purulla area. The late mafic eruption products and the Cerro Blanco volcanics are geologically classified as making up the Purulla Supersynthem. From the Miocene to the Pliocene the La Hoyada volcanic complex was active southwest of Cerro Blanco; afterwards came a 2 million years long hiatus. Cerro Blanco overlies this volcanic complex and outcrops of La Hoyada are found inside and around the calderas.