The first large eruption, which took place between 4 ± 0.9 and 5.3 ± 1.1 million years ago, formed the Toconao ignimbrite. The Toconao ignimbrite crops out mainly west of the caldera; only later were units of the Toconao identified on the eastern side of La Pacana. This ignimbrite has a volume of approximately and is formed by a lower un-indurated and an upper indurated subunit. Tube pumices are contained in the lower subunit and in a less than Plinian deposit that was emplaced beneath the Toconao ignimbrite.