Some differences exist between the facies of the ignimbrite inside and outside of the caldera, as well as between the western and eastern outcrops. Such differences concern the degree of welding of the ignimbrite, the occurrence or absence of devitrification and the jointing patterns. In fact, a segment of the northern Atana ignimbrite was later considered to not be actually part of the Atana ignimbrite at all because of the different facies and petrology. This separate ignimbrite was christened to be an upper and a lower Tara ignimbrite, possibly erupted by the Cerro Guacha caldera. The Tara ignimbrite fills part of the La Pacana caldera. The total volume of the La Pacana ignimbrites proper is estimated to be about , on the basis of gravimetric information about the volume of the caldera and the infill ignimbrites.