The main Payún Matrú massif formed in about 600,000 years, with the oldest trachytic rocks dated to 700,000 years ago. It is comprised by the lavic and ignimbritic Pre-caldera Trachyte unit and consists of trachyandesitic to trachytic rocks, with trachyte being the most important component. The massif may have formed a tall edifice like the Payun volcano before caldera collapse.