The Metalliferous Hills form the principal and most extensive hill and mountain area of the Tuscan Antiapennines. They stretch from the central-western part of Tuscany, involving four provinces, the south-eastern part of the province of Livorno, the southern part of the province of Pisa, the south-western part of the province of Siena and the north-western part of the province of Grosseto (the Metalliferous Hills of Grosseto).