Tralcán Formation (Spanish: Formación Tralcán) is a sedimentary formation of Triassic age in Los Ríos Region in south–central Chile.

The formation is named after Mount Tralcán on the western edge of Riñihue Lake.

The more than 800 metres (2,600 ft)[1] thick formation comprises reddish-grey conglomerates with a sandy matrix and intercalated reddish shales.

The shales of the formation contain abundant fossil flora.

Fossils of Cladophlebistenia oeshi have helped to redefine the age of the formation, that was formerly considered Late Jurassic (Kimmeridgian to Tithonian), to the Rhaetian of the Triassic.