 The 1972 constitution has been amended 31 times as of 2015.Major amendments include establishment of a reclamation trust (funded by taxes on natural resource extraction) to restore mined land (1974); restoration of sovereign immunity, when such immunity has been approved by a two-thirds vote in each house (1974); establishment of a 90-day biennial (rather than annual) legislative session (1974); establishment of a coal tax trust fund, funded by a tax on coal extraction (1976); conversion of the mandatory decennial review of county government into a voluntary one, to be approved or disallowed by residents in each county (1978); conversion of the provision of public assistance from a mandatory civil right to a non-fundamental legislative prerogative (1988); a new constitutional right to hunt and fish (2004); a prohibition on gay marriage (2004); and a prohibition on new taxes on the sale or transfer of real property (2010).In 1992, voters approved a constitutional amendment implementing term limits for certain statewide elected executive branch offices (governor, lieutenant governor, secretary of state, state auditor, attorney general, superintendent of public instruction) and for members of the Montana Legislature.