The South Spur edifice is the oldest structure found at Lastarria. The Negriales lava field formed later. The five craters of Lastarria proper formed in five different stages. An alternative view holds that Negriales formed before the South Spur, and that the main edifice formed in ten different stages. Block-and-ash flows, hot avalanches, lava domes, lava flows, and pyroclastic flows have all been involved in the activity of Lastarria. Most deposits on the northern slopes were erupted during the last two stages, with the exception of several exposures of the older stages on the northwestern flank and the western pink pyroclastic flow deposit. Overall, later and Holocene activity at Lastarria was highly explosive, unlike the more effusive earlier eruptions including the Negriales eruptions.