The Blue Mountains is a mountainous region in New South Wales, Australia. It borders on Sydney's metropolitan area, its foothills starting approximately 50 kilometres (31 mi) west of the state capital. The area begins on the west side of the Nepean River and extends westward as far as Coxs River. 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 of the range is Mount Werong at 1,215 metres (3,986 ft) above sea level. 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,The climate varies with elevation. At Katoomba, (1,010 m or 3,314 ft) the summer average maximum temperature is around 22°C with a few days extending into the 30s (80s–90s °F) although it is quite common to see maximum temperatures stay in the teens when east coast troughs persist. Night-time temperatures are usually in the teens but can drop to single figures at times. During winter, the temperature is typically around 10 to 11 °C in the daytime with −1 °C or so on clear nights and 3 to 4 °C on cloudy nights. Very occasionally it will get down to -3C or a little lower but usually the coldest air drains into the valleys during calm, clear nights. The Blue Mountains is not known for particularly cold mornings compared to other areas on the Central Tablelands like Oberon, Bathurst and Orange etc. There are two to three snowfalls per year although settled snow has become less common in recent decades. In the lower mountains, however, the climate is significantly warmer.
Annual rainfall is about 1,050 millimetres (41 in) in the Upper Blue Mountains,