The Aucanquilcha cluster formed in four stages, each corresponding to a group. The Alconcha group, with seven volcanoes, is constructed from pyroxene, andesite and dacite and formed 11-8 mya. It is constructed from two northern composite cones, Alconcha and Volcan Tuco (also known as Cerro Garage, dated 10.96-10.51 mya), and five lava domes on the northeastern side of the cluster. Alconcha has a large breach on the southern side of its crater that is likely the product of a flank collapse but the avalanche deposit may be buried beneath younger material. Lavas within the breach are dated 10.78-10.43 mya. The centres of Volcan Tuco and Alconcha are heavily eroded, and Alconcha's lavas and scoria lie on top of Tuco. The Ujina ignimbrite was erupted 9.4 mya from an unknown vent and has a volume of of dacite. While the vent location is unknown, the composition of the ignimbrite, and its dating and distribution, indicate an association with this group. The domes are poorly researched, with the Coscalito dome dated 8.9-8.7 mya and Cerro Amincha 8.01. The total volume of this group is , indicating a flux rate of .