San Pedro is part of the long Central Volcanic Zone, one of the two belts of volcanoes in Chile, which contains a total of about 44 active volcanoes plus silicic caldera and ignimbrite systems and monogenetic volcanoes. Many of these volcanoes are of Pliocene-Pleistocene age and approach heights of about above sea level at Llullaillaco and Ojos del Salado; such sizes of the volcanoes occur because the edifices rise from a relatively high basement. Volcanism in this region is relatively poorly studied and there is not much present-day activity; with the exception of Láscar, most present-day manifestations are limited to fumarolic activity.
