Open Space Subvention Act


The Open Space Subvention Act (OSSA) was enacted on January 1, 1972, to provide for the partial replacement of local property tax revenue foregone as a result of participation in the Land Conservation (Williamson) Act and other enforceable open space restriction programs (Government Code §16140 et seq.). Participating local governments received annual payment on the basis of the number of eligible acres, quality (soil type and agricultural productivity), and, for Farmland Security Zone contracts, location (proximity to a city) of land enrolled under eligible enforceable open space restrictions.

Open Space Subvention Payments

Open Space Subvention payments totaled more than $863 million between 1972 and 2010.  Despite elimination of OSSA payments since the FY 09/10 budget, Williamson Act enrollment information provided by counties and cities is critical in order to document the level of participation in the program and the impact the loss of OSSA payments is having on local governments. Enrollment information was the basis for the biennial Land Conservation Act Status ​Report, which provided information to the Legislature and general public on the status of the Program among counties and cities.

The recent passage of Senate Bill 574 has simplified Williamson Act reporting requirements​, and eliminated the biennial Land Conservation Act Status Report. Enrollment information will now be collected in Geographic Information System form, and will be made public on the Department's website biennially. ​More information and statistics are available on the Reports and Statistics page.
Open Space Subvention Survey​ - Now Available

The 2021​ Survey of Participation in the Williamson Act and Open Space Subvention Act (OSSA) is now available.​

2021 Open Space Subvention Survey ​(Excel spreadsheet) 

​Please see the instructio​ns for completing and submitting forms (PDF) and the Frequently Asked Questions​ handout​ (PDF) for additional help.

Annual Survey of Participation forms are due to the Department of Conservation by October 31, 2021.   

If you have any questions or problems with the survey form, please contact Farl Grundy, Environmental Planner via email at​ In the Departments continuing effort to migrate to a paperless environment, all documents can be emailed to the Department at

Web Accessibility Statement. If you find any part of an above document​ to be inaccessible with assistive technology, visit our Accessibility web page at to report the issue and request alternative means of access. To help us respond to your concern, please include in your request: your contact information, the title of the document, and the web address where you obtained it.