 The first stage occurred between 5.60 and 4.51 million years ago and consisted of the eruption of large ignimbrites such as the Blanco, Cueva Negra, several Merihuaca ignimbrites and Real Grande ignimbrite as well as lava domes, all from north-south trending fractures, forming the Toconquis Group (formerly called the Toconquis Formation).The Real Grande and Cueva Negra ignimbrites were considered to be homologous, as are the easterly Leon Muerto and several Merihuaca ignimbrites, but it was later found that the Leon Muerto and Merihuaca ignimbrites probably were erupted from distinct vent systems and have distinct compositions, and the Cueva Negra ignimbrite was later considered to be a separate formation from the other Toconquis group ignimbrites.The later classifications established a 6.5 5.5 million-year-old Blanco/Merihuaca ignimbrites, 4.8 million-year-old Pitas, 4.7 million-year-old Real Grande, 4.5 million-year-old Vega and 3.8 million-year-old Cueva Negra ignimbrite.