OAKLEY -- An agriculture conservation group recently presented the city with information about its vineyards that's expected to help decision-makers preserve as much of Oakley's agrarian heritage as possible while continuing to develop.

The Agricultural-Natural Resources Trust shared the results of an inventory that it had taken of parcels where farmers are growing grapes -- 723 acres all told.

The nonprofit also studied Oakley's general plan, which depicts where the city intends to allow residential and commercial development over the long term.

In addition, ANRT used maps that the state creates to identify the location and number of parcels it considers important farmland, a designation that many of Oakley's vineyards have.

By overlaying the three sets of information, the organization has enabled city officials to see more easily not only where vineyards are located but which of those parcels the state considers valuable -- information the city didn't have ready access to before -- and the extent of development their land-use designation allows.

If, for example, a vineyard is in an area zoned for a certain number of homes but that land also is deemed important by the state, the city knows that it needs to alert potential buyers to that caveat.

"We can tell developers what mitigations they'll have to do if they purchase and develop the property," Councilman Kevin Romick said. "This information provides a way for our staff to help the developer makes choices about whether they want to proceed based on protections that were placed by the state."

Romick noted that developers often must offset the loss of agricultural land in a 1-to-1 ratio: For every acre they build over, they have to replace it by buying the same amount of open land elsewhere and agree to keep it that way.

ANRT's mapping exercises also helped the city identify three large clusters of vineyards that it now will focus on preserving, Romick said.

Concentrating on these areas makes the most sense because it's easier getting grant money to pay growers for keeping their property off-limits to development when larger parcels of land are involved, he said.

He added that ANRT is negotiating with at least one of those vineyards' owners to restrict the use of that land to agricultural production.

The Oakley City Council agreed that it wouldn't place a mitigation fee on developers because it wouldn't generate enough revenue for the city either to buy farmland itself and spare it from development, or pay farmers to give up their development rights.

As such, the next phase of the project will consist of the council looking for other sources of money to finance an agriculture mitigation program.

Romick emphasized that growers' participation in the program is strictly voluntary; it's ultimately up to them whether they accept the city's offer or cash out their land to developers.

"It's important (for them) to know that we can't force someone to sell their property (to the city)," he said.

Contact Rowena Coetsee at 925-779-7141. Follow her at Twitter.com/RowenaCoetsee.