 Cerro Azul , just 7 kilometres ( 4 @.@ 3 mi ) south of Descabezado Grande volcano , is part of the Descabezado Grande – Cerro Azul eruptive system , a volcanic field which comprises its two large namesake volcanic edifices and several smaller vents , including 12 Holocene calderas . Both volcanoes lie on top of the Casitas Shield , a plateau built of over 100 lava flows that erupted in at least 12 volcanic episodes during the Quaternary period . The upper lava layers are dated at 340 @,@ 000 years . 
