 Much of the swampy isthmus is drained by San Tadeo River that flow in SSW direction to the Gulf of San Esteban.Geologically it is considered the southern end of the Chilean Central Valley, and the Liquiñe-Ofqui Fault.The Isthmus of Ofqui lies close to the Chile Triple Junction where the Nazca Plate, the South American Plate, and the Antarctic Plate meets.