Río Frías Formation

Río Frías Formation (Spanish: Formación Río Frías) is a Middle Miocenegeologic formation made up sedimentary rock located in Aysén Region, western Patagonia. The formation crops out along the upper course of Cisnes River (Spanish: Río Cisnes). Marsupial fossils have been found in the formation. The Friasian period in the South American Land Mammal Ages is named after the formation.