The Biobío River is the second largest river in Chile. It originates from Icalma and Galletué lakes in the Andes and flows 380 km to the Gulf of Arauco on the Pacific Ocean.

The Central Valley, Intermediate Depression, or Longitudinal Valley is the depression between the Chilean Coastal Range and the Andes Mountains. The Chilean Central Valley extends from the border with Peru to Puerto Montt in southern Chile, with a notable interruption at Norte Chico. South of Puerto Montt the valley has a continuation as a series of marine basins up to the isthmus of Ofqui. Some of Chile's most populous cities lie within the valley including Santiago, Temuco, Rancagua, Talca and Chillán.