Tidbinbilla Nature Reserve is a 54.5 square kilometres (21.0 sq mi) protected area, on the fringe of Namadgi National Park, that is a short drive from the city of Canberra, in the Australian Capital Territory, the capital city of Australia. The nature reserve consists of a large valley floor, the Tidbinbilla Mountain and the Gibraltar range. The sides of the valley are steep and relatively undisturbed; the lower slopes are partly cleared and have a history of Aboriginal and European use. Tidbinbilla Mountain is believed to have been used for initiation ceremonies. The word 'Tidbinbilla' is Aboriginal in origin and is derived from the word Jedbinbilla – a place where boys become men.