The Crete Senesi are the area south-east of the city of Siena, which includes the municipalities of Asciano, Buonconvento, Montalcino (part of the former municipality of San Giovanni d'Asso, Monteroni d'Arbia, Rapolano Terme, and Trequanda, all in province of Siena. The name derives from the clay, or clay, present in the ground, which gives the landscape its characteristic gray-blue color and an appearance often described as lunar. This characteristic clay, mixed with rock salt and gypsum, called mattaione, represents the sediments of the Pliocene sea which covered the area between 2.5 and 4.5 million years ago.The landscape is characterized by barren and gently undulating hills, solitary oaks and cypresses, isolated farms on top of the woods in the valleys, the fountains that collect rainwater.Typical conformations of the land are the gullies, the crags and the biancane. Inside the Crete Senesi there is the semi-arid area known as the Accona Desert where these formations occur more frequently.