Activity commenced in the Miocene with basaltic andesites and dacitic ignimbrites and ended in the late Quaternary with basaltic andesites in form of cinder cones. K-Ar dates of 12 mya and 8.0 ± 0.3 have been found at Cerro Negro. Lava flows found on Escorial and Cerro Corrida de Cori are the latest volcanic events and post-date the hydrothermal alteration; one date from Escorial is 0.342 ± 0.025 mya. Most Escorial lava flows head southwest. These Escorial lava flows are accompanied by andesitic blocks from possibly Vulcanian explosive activity. East of Corrida de Cori range a cinder cone accompanied by a much smaller vent was constructed on top of older eruption products and generated a lava flow that descended towards Salar Rio Grande. This cone may be of Holocene age, considering the appearance of the blockly lava flows. Present day geothermal activity is found at Lastarria and in form of fumarole spires, mud vents and warm springs at Escorial. Some of these originate by the summit lava flow of Cerro Escorial.