They occur in the wider region of Chachani and crop out in the Arequipa area and in river valleys. Their emplacement took place in the form of fast-moving hot streams of rock. An additional ignimbrite is the 13 million years old Miocene Rio Chili Ignimbrite; the vents of the Miocene units are unknown and the Rio Chili Ignimbrite appears to be related to the Huaylillas Ignimbrite of southern Peru.