The Ag Preserve in Paso Robles California and surrounding areas, commonly referred to as the "Williamson Act",  is a property tax relief measure for owners of farmland including vineyards. The act permits a landowner, whose land is used for farming, to sign a contract with Monterey, San Luis Obispo or Santa Barbara County to guaranteeing that the land will continue to remain in farming for a period of at least 10 years.

In return for this guarantee, the Assessor annually values land and growing improvements in the Act using a restricted income approach rather than the market value.  The farmer gets the benefit of being taxed on the lower of the total base year value, current market value, or restricted (AG Preserve) value.  Generally, this means the taxes for the farmer or vineyard owner are reduced, sometimes greatly.

Property owners must apply to the County Planning Department to receive Williamson Act benefits.  The Assessor's Office may require you to report data pertaining to your agriculture parcels via an AG Preserve Questionnaire.