Volcanic activity in the Chachani region appears to have begun during the Cretaceous-Paleocene in the form of the Toquepala volcanics. The oldest volcanic rocks of the Western Cordillera are known under the name Tacaza, and underwent erosion and folding before the next phase which is known as Sillapaca. Finally, during the Miocene-Quaternary the Sencca Formation and the Barroso volcanics developed; Chachani is classified as part of the Barroso volcanics although the oldest volcanism might belong to the Sillapaca unit.