The Pajonales-Pular volcanic massif is formed by andesitic and dacitic rocks and covers an area of on faulted Miocene sediments. The massif consists of an alignment of volcanoes and two subunits, a heavily eroded unit that consists of Pajonales and Pular proper and a younger unit consisting of volcanic domes. These domes reach heights of and one of these overlies a glacial moraine. Rocks of the older unit are 3.9 million years old, while one of the domes has been dated to be 1.8 million years old.