Potassium-argon dating and argon-argon dating performed on rocks from the Chao I stage have indicated an average age of 423,000 ± 100,000 years. However, anomalous chemical compositions of the dated rocks suggest that they may overestimate the true age of the volcanics. Such alteration may be the result of the inclusion of xenocrysts or K leaching. A glacial moraine system lies on Cerro del León at altitude. One of these moraines abuts Cerro Chao, indicating that the dome must be older than the moraine and thus older than the last glaciation 11,000 years ago. An active magmatic body may still exist under Cerro Chao and Paniri.