The Upper Valdarno Basin is famous for its fossils of animals and plants. The history of the basin is complex. Two lacustrine phases can be distinguished, which are partly overlain by fluviatile and partly by fan-deposits. These depositional phases range in time from Middle Pliocene to Middle or Late Pleistocene and are separated by phases of non-deposition and erosion. The geological history of the basin, its fossil faunas and their stratigraphical ages are discussed below.