The 170 metres (560 ft) thick formation comprises tuffaceous mudstones and sandstones deposited in a crater lake environment and crops out at Laguna del Hunco in the northwestern Chubut Province.

The approximately 170 metres (560 ft) thick formation forms part of the Middle Chubut River Volcanic Pyroclastic Complex of the western Cañadón Asfalto Basin.

The complex is characterized by a great variety of volcanogenic bodies, such as ignimbrites, domes, lava flows, necks, intrusives, tuffs, and volcaniclastic deposits (of predominantly lacustrine origin), all of them frequently interbedded.

[12] The floral assemblage is thought to represent a lakeshore vegetation,[2] deposited during the Early Eocene Climatic Optimum (EECO),[13][14] with estimated average yearly temperatures of 17.2 ± 2.3 °C (63.0 ± 4.1 °F) and annual rainfall of 1,673 ± 426 millimetres (65.9 ± 16.8 in).

[13] The following fossil plants and animals have been described from the formation: Aves Ueekenkcoracias tambussiae Amphibia Shelania pascuali Austropanorpodes gennaken Austroperilestes hunco Chinchekoala qunita Frenguellia iglesiasi Frenguellia patagonica Huncoaeshna corrugata Satelitala soberana Urocerus patagonicus Paleoovoidus arcuatum Paleoovoidus bifurcatus Paleoovoidus rectus Araucariaceae Araucaria pichileufensis Cycads Austrozamia stockeyi Cunoniaceae Ceratopetalum edgardoromeroi Escalloniaceae Escallonia Ginkgoaceae Ginkgo patagonica Gymnostoma archangelskyi Gymnostoma argentinum Gymnostoma patagonicum Lomatia occidentalis Lomatia preferruginea Osmundaceae Todea amissa Podocarpaceae Podocarpus andiniformis Ripogonaceae Ripogonum americanum Solanaceae Physalis infinemundi Malvaceae Uiher karuen