The Cumberland Plain, an IBRA biogeographic region, is a relatively flat region lying to the west of Sydney CBD in 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, and it is a structural sub-basin of the Sydney Basin. The Cumberland Plain has an area of roughly , which lies on Triassic shales and sandstones. Shaping the geography of Sydney, it extends from 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. The Hornsby Plateau is located to the north and is dissected by steep valleys. The plain takes its name from Cumberland County, in which it is situated, one of the cadastral land divisions of New South Wales. The name Cumberland was conferred on the County by Governor Arthur Phillip in honour of Ernest Augustus, Duke of Cumberland. Being the most populous region in Australia, the Cumberland Plain is one of the fastest-growing areas of the country in terms of population and it is home to a variety of Australian animal species, which are observable in the urban environments. Geography The Cumberland Plain stretches from Ryde in the east to the Nepean River in the west and from Cattai in the north to Thirlmere in the far south. The Cumberland Plain sprawls over south-western Sydney, and into the Greater Western Sydney area. It is within the local government areas of Blacktown, Burwood, Camden, the western portion of Campbelltown, Canada Bay, Canterbury-Bankstown, Cumberland, Fairfield, Georges River, Hawkesbury, the Western outskirts of the Inner West Council, Liverpool, Parramatta, Penrith, Ryde, Strathfield, The Hills Shire, Wingecarribee, and Wollondilly. The rest of the Sydney regions such as Sydney CBD (including the City of Sydney), North Shore, Northern Beaches, Eastern Suburbs, Southern Sydney (including Sutherland Shire), Hills District, Hornsby Shire and the Forest District do not lie in the Cumberland Plain. The region mostly consists of low rolling hills and wide valleys in a rain shadow area near the Blue Mountains. The annual rainfall of the plain is typically around 700–900 mm, and is generally lower than the elevated terrain that partially surrounds it. Common vegetation in the Cumberland Plain is eucalyptus trees. Soils