Rock formations in the region include the Mesozoic Yura Group sediments, the Toquepala intrusive rocks, the 30-24 million years old Tacaza volcanic rocks, the 24-10 million years old Huaylillas volcanic rocks and the 10-3 million years old Barroso volcanic rocks; Purupuruni is considered to be part of this Barroso formation. Purupuruni and neighbouring volcanic centres have formed on the Cretaceous sedimentary basement.