The GREAT BARRANCA, east of the town of Sarmiento, Province Chubut, Patagonia, Argentina. Exposure of terrestrial Paleocene (early Tertiary) sedimentary rocks. 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). The cliffs shown on this photo are from the Rio Chico Formation (Tertiary, Paleocene)