http://www.consrv.ca.gov/DLRP/lca/
Williamson Act Program
The California Land Conservation Act of 1965—commonly referred to as the Williamson Act—enables local governments to enter into contracts with private landowners for the purpose of restricting specific parcels of land to agricultural or related open space use. In return, landowners receive property tax assessments which are much lower than normal because they are based upon farming and open space uses as opposed to full market value. Local governments receive an annual subvention of forgone property tax revenues from the state via the Open Space Subvention Act of 1971.
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Fact sheet (PDF)
http://www.consrv.ca.gov/DLRP/lca/pubs/WA%20fact%20sheet%2006.pdf
Q&A
Williamson Act Program
Open Space Subvention Act
http://www.consrv.ca.gov/DLRP/lca/ossp/questions_anwers.htm