The geological substratum of the Park area is generally Granodiorite, an igneous rock. Except for recent sediments and volcanic cinders, no old sedimentary rocks appears anywhere in the Park. Through the igneous rock substratum, a number of stratovolcanoes have emerged. The Tronador and related structures are the result of volcanic activity dating back to the early Pleistocene. At the western entrance to the Park, the symmetrical cone of the Osorno volcano forms a towering landmark over the Todos los Santos and Llanquihue lakes. The peak of the Osorno is at . The Osorno built up on top of an older stratovolcano, La Picada, which has a 6-km-wide caldera now mostly buried. The Puntiagudo is a stratovolcano with a sharp peak whose summit is at . From the Puntiagudo to the northeast for extends a fissure that has given birth to 40-odd basaltic scoria cones. The Cayutue La Vigueria volcanic field consists of some 20 maars and cinder cones, of which Volcan Cayutue is the principal. The activity of Volcan Cayutue filled the Cayutue depression and separated the Todos los santos lake from the Ralun estuary. Lava flows from these volcanoes is basaltic and andesitic. Their activity is generally explosive and lava flows are highly viscous. A summary of scientific information on the volcanoes of the Park (Osorno, Puntiagudo-Cordón Cenizos and La Viguería) is available from the Global Volcanism Program of the Smithsonian Institution.