The Cornia Valley is the southern part of the province of Livorno, opening in the area straddling the Maremma livornese and Maremma grossetana near the mouth of the eponymous River. The area is mostly hilly inland where it creeps towards the southwestern foothills of the metalliferous hills and enters in the southern part of the province of Pisa; is flat along the coastal strip, with the exception of the Piombino promontory which separates the city from the Gulf of Baratti.