The principal sector collapse occurred after the Ch'aska Urqu stage. It was followed by the eruption of andesitic lava flows and the compound lava dome in the summit region, all focused into the collapse scar; this focusing is a phenomenon noted at other volcanoes which underwent flank collapses such as Planchón-Peteroa. This formation has been named the Santa Cecilia series. The compound summit lava dome probably fills the collapse scar but young lavas and glacial erosion make this assessment difficult. Dates obtained on the summit lava domes range from 220,000 ± 50,000 years ago to 130,000 ± 40,000 years ago. The youngest date was obtained on the youngest dome and shows an age of 65,000 years ago. Tephras identified in the Salar Grande close to the Pacific coast and dated to be less than 330,000 years old may come from Ollagüe or Irruputuncu.