The Cumberland Plain is the surface expression of the Cumberland Basin of New South Wales, Australia. Cumberland Basin is the preferred physiographic and geological term for the low-lying plain of the Permian-Triassic Sydney Basin found between Sydney and the Blue Mountains. The Cumberland Plains has an area of roughly 2750 km2. The plain extends from 10 kilometres north of Windsor in the north, to Picton in the south; and from the Nepean-Hawkesbury River in the west almost to Sydney City's Inner West in the east. Much of the Sydney metropolitan area is located on the Plain.