The Blue Mountains is a mountainous region in New South Wales. It borders on Sydney's metropolitan area, its foothills starting approximately 50 kilometres west of the state capital. The public’s understanding of the extent of the Blue Mountains is varied, as it forms only part of an extensive mountainous area associated with the Great Dividing Range. Officially, the Blue Mountains is bounded by the Nepean and Hawkesbury Rivers in the east, the Coxs River and Lake Burragorang to the west and south, and the Wolgan and Colo Rivers to the north. Geologically, it is situated in the central parts of the Sydney Basin.
Consisting mainly of a sandstone plateau, the area is dissected by gorges up to 760 metres (2,490 ft) deep. The highest point in the Blue Mountains, as it is now defined, is an unnamed point with an elevation of 1189m (3902ft) seven kilometres north-east of Lithgow. However, the highest point in the broader region once considered to be the Blue Mountains is Mount Bindo, elevation 1362m (4470ft). A large part of the Blue Mountains is incorporated into the Greater Blue Mountains Area World Heritage Site, consisting of seven national park areas and a conservation reserve.
The Blue Mountains area includes the local government areas of the City of Blue Mountains, the City of Hawkesbury, the City of Lithgow and Oberon.