The Chattian (also known as Chickasawhayan or Late Oligocene) is the second and final of two stages of the Oligocene Epoch. It spans the time between 28.4 ± 0.1 Ma and 23.03 ± 0.05 Ma (million years ago). During the Chattian the largest known single-event volcanic eruption occurred: the Fish Canyon eruption of La Garita with a magnitude of 9.2. It has been dated to 27.51 Ma ago. The Chattian stage spans the Mammal Paleogene zones 26 through 30 and part of 25.