The Great Barranca - exposure of terrestrial Paleocene (early Tertiary) sedimentary rocks. . East of the town of Sarmiento, Province Chubut, Patagonia, Argentina. In the words of a paleontologist, 'it is the most imposing and important single known fossil mammal locality in South America, and one of the most important in the world' (George Gaylard Simpson, 1984).Dark smooth hills: Salamanca FormationMiddle yellow/red cliffs: Rio Chico FormationTop whitish layers: Sarmiento Formation.