The Cerro Blanco volcanic system has been active during the Pleistocene and Holocene. The oldest volcanic rocks related to Cerro Blanco are the over 750,000 years old so-called Cortaderas Synthem; its outcrops are limited to an area Laguna Carachipampa. It consists of two ignimbrites, the Barranca Blanca Ignimbrite and the Carachi Ignimbrite, which were erupted a long time apart. The former is a massive, white, unwelded ignimbrite, the latter is massive, rose-coloured and weakly welded. They contain pumice and fragments of country rock and consist of rhyodacite unlike later units. These ignimbrites, whose chronological relation to each other is unknown, were probably produced by boil-over of a volcanic vent rather than by an eruption column. Their exact source vent is unknown.