The basement beneath La Pacana is formed by sediments of Ordovician age, Devonian-Permian quartzites, the mixed Salta formation also of Permian age and sediments of Cretaceous-Tertiary age. At the eastern margin of La Pacana in Argentina, they overlay an even older Precambrian basement. Most of this original basement however is covered by Miocene ignimbrites from centres that may coincide with the La Pacana caldera. Two of these older ignimbrites are known as the Pampa Múcar and Antigua Chacaliri ignimbrites.