The first volcanic activity occurred west and east of Payún Matrú and involved the emission of olivine basalt lava flows. The long Pampas Onduladas lava flow was erupted 373,000 ± 10,000 years ago and buried parts of the 400,000 ± 100,000 years old Los Carrizales lava field; both have hawaiitic composition. The Payun volcano formed around 265,000 ± 5,000 years ago within a timespan of about 2,000-20,000 years. Its inferred eruption rate of is similar to typical volcanic arc eruption rates such as at Mount St. Helens.