The 'Crete senese' (Literally “Senese clays”) refers to the residual sediment left from the Pliocene era. The crete can look alpine in areas of steep elevation or in the rolling hills where crops are cultivated and after the earth has been turned over post-harvest, the light grey color of the fields recalls the light grey of the lunar surface.
You can take the train from Siena or Grosseto.