Planning for opening the 1,100-acre Taylor Mountain open space purchase as a regional park got underway Tuesday when Sonoma County supervisors approved spending $438,000 on a master plan.

The park, assembled through four separate land purchases by the Agricultural Preservation and Open Space District between 1995 and 2005, could be opened by 2012.

The Taylor Mountain acquisition, so big that it spreads into two supervisorial districts, is one of the district's most notable in terms of creating parkland between southeast Santa Rosa and Bennett Valley.

"It is in a prime area in our county in terms of access and usage," said board chairwoman Valerie Brown.

"It is an absolute gem," said Supervisor Shirlee Zane.

The parkland stretches from Petaluma Hill Road to Bennett Valley Road and its northwest corner will host a small section of the proposed Farmers Lane extension.

After heaping accolades on the open space district for securing the Taylor Mountain land for a total of $21 million, supervisors approved a planning contract with RRM Design Group to establish a framework for park development.

The California-based firm with regional offices in Oakland has designed projects ranging from Roseland redevelopment to downtown Cloverdale. The company was one of nine consulting firms that bid on the park planning process, which will take about two years to complete and incldues public comment sessions and environmental studies.

The open space district intends to turn the property over to the county regional parks departments later this year, said Sara Press, an associate open space planner.

"It is the dominate feature of the Santa Rosa Plain," she said.

Currently, much of the land is leased for cattle grazing, and the LandPaths conservation group has supervised issuance of about 1,000 special permits for limited public access. LandPaths is on target to issue another 1,500 special permits over the next year through orientation sessions conducted in Spanish and English, Press said.

Since the quarter-cent sales tax to fund the open space district was overwhelmingly reauthorized by voters in November 2008, supervisors and open space advocates have worked to balance the growing clamor for access with funding for parkland maintenance and operations.

"The sooner we can get it open for public access the better," Supervisor Paul Kelley said.