Blue Mountains

The Blue Mountains are a mountainous region and a mountain range located in New South Wales, Australia. The region is considered to be part of the western outskirts of the Greater Sydney area. The region borders on Sydney's main metropolitan area, its foothills starting about west of centre of the state capital, close to Penrith. 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. As defined in 1970, the Blue Mountains region 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. The Blue Mountains Range comprises a range of mountains, plateau escarpments extending off the Great Dividing Range about northwest of Wolgan Gap in a generally southeasterly direction for about , terminating at . For about two-thirds of its length it is traversed by the Great Western Highway, the Main Western railway line and the soon to be completed, Blue Mountains tunnel. Several established towns are situated on its heights, including Katoomba, Blackheath, , and . The range forms the watershed between Coxs River to the south and the Grose and Wolgan rivers to the north. The range contains the Explorer Range and the Bell Range. The Blue Mountains area includes the local government area of the City of Blue Mountains. Since the early 2010s, the region's biodiversity and infrastructure has been severely affected by massive bushfires of unprecedented size and impact. In 2018 8.4 million people visited the Blue Mountains. The Blue Mountains and Southern Highlands Basalt Forests is a prominent forest community within the ecoregion. Etymology Following European settlement of the Sydney area, the area was named the Carmarthen and Lansdowne Hills by Arthur Phillip in 1788. The Carmarthen Hills were in the north of the region and the Lansdowne Hills were in the south. The name Blue Mountains, however, was preferred and is derived from the blue tinge the range takes on when viewed from a distance. The tinge is believed to be caused by Mie scattering which occurs when incoming light with shorter wavelengths is preferentially scattered by particles within the atmosphere imparting a blue-greyish colour to any distant objects, including mountains and clouds.