Like the upper Valdarno, the area of Reggello is typified by geological structures of particular charm and beauty that consist of various sorts of sand, clay and stratified gravel. These structures, which are known as Balze [crags], have steep vertical walls and rise to a height of hundreds of metres in a succession of different forms interspersed with deep ravines. The Balze border the tableland with an almost uninterrupted frame that is characterised by a typical yellow-ochre colour. They constitute a cutaway view of natural history of great value, one which recalls the geological history of the territory. The appearance of the Balze is, in fact, the result of an erosion of the leaching waters on the ancient sediments of the Pleistocene lake that occupies the valley of the Arno river. In addition to providing spectacular landscape scenery, the Balze have a heterogeneous habitat that offers a sanctuary to numerous species of birds, mammals and insects. The floristic landscape is also varied: herbaceous plants flower on clay, while shrubs and trees grow on the different types of sand.