"The Crete Senesi refers to an area of the Italian region of Tuscany to the south of Siena. It consists of a range of hills and woods among villages.
Crete senesi are literally ‘Senese clays’, and the distinctive grey colouration of the soil gives the landscape an appearance often described as lunar. This characteristic clay, known as mattaione, represents the sediments of the Pliocene sea which covered the area between 2.5 and 4.5 million years ago. " (Wikipedia)
From Italian Landscapes