Williamson Act

The California Land Conservation Act (Williamson Act) was enacted by the State Legislature in 1965 as a means of preserving California's Prime agricultural lands from urbanization. Since it was enacted, the Act has been amended several times to allow its use not only to protect prime agricultural lands, but most other types of open space lands as well.
The Williamson Act involves voluntary contracts between landowners and a city or county in which they agree to retain their lands in agriculture or other open space uses for a minimum of ten years. In return for entering into this contract, the landowners receive property tax relief on the lands under contract. This relief is provided through the assessment of the lands based upon their income-producing value rather than their market value, which may be considerably higher.
The contracts have a ten-year term which are automatically renewed each year on a common anniversary date of January 1 unless they are canceled or notice of non-renewal is given. If notice of non-renewal is given by either party to a contract, the non-renewal process begins on the following anniversary with nine years remaining. During the remaining term of the contract after notice of non-renewal has been given, the property taxes increase gradually according to a formula that eventually brings them up to the same level as non-Williamson Act lands.