The California Land Conservation Act, better known as the Williamson Act, has been the state’s premier agricultural land protection program since its enactment in 1965. The Williamson Act preserves agricultural and open space lands through property tax incentives and voluntary restrictive use contracts. Private landowners voluntarily restrict their land to agricultural and compatible open-space uses under minimum 10-year rolling term contracts with local governments. In return, restricted parcels are assessed for property tax purposes at a rate consistent with their actual use, rather than potential market value.
California Department of Conservation, "The California Land Conservation (Williamson) Act 2010 Status Report" (2010). California Agencies. Paper 396.