It ended four decades of disputes over the shape and design of Lake Burley Griffin, the centrepiece of Canberra, with construction completed in 1964. This prompted the development of the Parliamentary Triangle, a core part of Griffin's design, and followed various buildings of national importance were constructed on the lakefront. On average, the population of Canberra increased by more than 50% every five years between 1955 and 1975. More residential land was released through the creation of new town centres in the 1960s and 1970s. An elective Advisory Council was created for the ACT in 1930. It was replaced by a House of Assembly in 1974. Full self-government was granted in 1988, with the Legislative Assembly electing the Chief Minister of the Australian Capital Territory to serve as the territory's head of government. The assembly has most of the powers and responsibilities of state governments, but its actions are subject to a federal veto. The ACT gained a seat in the House of Representatives in 1949, initially with limited voting rights. It has had multiple members since 1974, and since 1975 has also elected two members of the Senate. Indigenous prehistory Indigenous Australian peoples have long inhabited what is now the ACT. Anthropologist Norman Tindale has suggested the principal group occupying the region were the Ngunnawal people, while the Ngarigo and Walgalu lived immediately to the south, the Wandandian to the east, the Gandangara to the north, and the Wiradjuri to the north-west. Archaeological evidence from the Birrigai rock shelter in Tidbinbilla Nature Reserve indicates habitation dating back at least 21,000 years. It is possible that the area was inhabited for considerably longer, with evidence of an Aboriginal presence in south-western New South Wales dating back around 40,000–62,000 years. Another site of significance in the reserve is the Bogong Rocks shelter, which contains the oldest evidence of Aboriginal occupation at a bogong moth resting site. These insects were an important source of food for the Aboriginal peoples of the Southern Alps and would accumulate by the thousands in caves and rock crevices, where they were collected and later roasted in sand or ashes, and then eaten whole. Numerous other culturally significant and archaeologically notable sites are known across the territory, including shelters, rock art sites, stone artefact scatters, scarred trees and chert quarries. Tidbinbilla Mountain is believed to have long been used for Aboriginal initiation ceremonies. 19th century exploration Following