Malleco Formation () is a geological formation of volcanic origin in the Andes of Araucanía Region (38–39° S), Chile. The formation is made up by volcaniclastic rocks, including tuffs, lahars and lavas of Pliocene–Early Pleistocene age.Suárez, M. and Emparan, C. (1997). Hoja Curacautín, Carta geológica de Chile. It is considered equivalent to the Cola de Zorro Formation found further north in Chile and the so-called "Asociación volcánica de la precordillera oriental" located around the upper courses Bío Bío and Aluminé rivers.
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