Save Mount Diablo has defended the Tassajara Valley and surrounding hills for over two decades.

This rural area just east of Danville and San Ramon, characterized by rolling grassland and the important Tassajara Creek riparian corridor, is an agricultural buffer between protected open spaces in every direction.

A Long, Embattled History

The public’s first major victory here was stopping the massive “Tassajara Valley Owners Property Association” project in the late 1990s.

Under the leadership of former Contra Costa County Supervisors Donna Gerber and Joe Canciamilla, Save Mount Diablo, the Sierra Club, Greenbelt Alliance, and hundreds of residents helped stop thousands of units proposed in the 4,900-acre project.

Then in 2000, we worked together to tighten the Contra Costa County Urban Limit Line (ULL: a line beyond which urban-style development can’t occur) to place the Tassajara Valley and other places outside the line, increasing their protection.

In 2004, when Contra Costa County’s transportation sales tax, Measure C, came up for renewal as Measure J, activists including Save Mount Diablo successfully included a provision that the county and all cities adopt voter-approved ULLs.

In 2006, county voters and every city including San Ramon once again approved an Urban Limit Line, with the Tassajara Valley outside the line.

In 2007, the “New Farm” project proposed to build 186 houses and a cemetery over 771 acres of the Tassajara Valley.

Developers proposed to do the project by changing the definition of what “urban” development is. If people accepted that development beyond the ULL wasn’t “urban,” then it wouldn’t matter if it was on one side of the line or the other.

Thanks to the work of Save Mount Diablo, concerned officials, and valley and nearby city residents, no one was fooled. So much resistance was generated that the developer would later table “New Farm.”

In 2010, we achieved a great victory in San Ramon against Measure W, which would have greatly expanded San Ramon’s Urban Limit Line to include the Tassajara Valley and allow housing subdivisions over the whole area.

With the help of San Ramon residents, we crushed it, with 72 percent of voters saying “no” to developing 1,600 acres of the Tassajara Valley.

Besides massive housing projects, there was also a cemetery proposed on 220 acres of the valley. Creekside Memorial Cemetery would have impacted rare plant and animal species, as well as the valley aquifer.

The local community was so concerned that when Save Mount Diablo led a hike in the summer of 2014 against this project, about 500 people, including local ranchers, showed up to signal their opposition! The cemetery project has been quiet for several years.

Tassajara Parks Approved: 28 Square Miles of Protection

The same developer that proposed “New Farm” has worked for years on a very different project, “Tassajara Parks.”

In 2013, “New Farm” was tabled, and the developer began meeting with Save Mount Diablo, cities, and other stakeholders to see if a compromise could be reached.

He would get a return on his investment, and we could greatly benefit the public by dramatically reducing project impacts and threats to the Urban Limit Line.

The eventual result was the Tassajara Parks project: a 30-acre adjustment of the county’s Urban Limit Line to accommodate a 125-unit housing development that would be placed next to existing development and the current ULL.

To adjust the Urban Limit Line, the county would have to make findings proving that the project would yield a lot of public benefits.

To show public benefits, we advocated for and won the creation of the 17,600+ acre Tassajara Agricultural Preserve, and the protection via dedication of 727 acres of open space (land that the developer owned but would not develop).

Thirty acres developed to 727 acres of open space protected is a massive protection ratio that provides far more benefits to wildlife, habitat, and the public than loss. And that’s before taking into account the nearly 18,000-acre agricultural preserve.

After eight years of work by Save Mount Diablo, on Tuesday, July 13, 2021, the Contra Costa Board of Supervisors approved the 125-unit Tassajara Parks project.

With a four-to-one vote, the Board adjusted the Urban Limit Line by 30 acres (in red) and created the 17,666-acre Tassajara Agricultural Preserve (in light green).  They also dedicated 727 acres (green diagonal lines) to the East Bay Regional Park District.

The 727-acre dedication is the highest mitigation ratio we have ever achieved. For every one acre moved within the Urban Limit Line, 24 acres were dedicated. Our second highest mitigation ratio was Magee Preserve in Danville, at 13:1.

However, the real prize is the Tassajara Agricultural Preserve. There are 17,666 acres (27.6 square miles) in which Contra Costa County and San Ramon have agreed not to allow annexations or General Plan amendments in the preserve, and which will be incorporated into their General Plans.

We now have a double layer of protection over the Tassajara region: the Urban Limit Line and the Tassajara Agricultural Preserve.

Above: Map of the proposed Tassajara Parks project site area (marked by translucent green with yellow boundary line), including existing protected open space (marked in solid green).

Tassajara Parks Overturned, but Increased Protection Remains

The County Board of Supervisors fulfilled all requirements, including the creation of the Tassajara Valley Agricultural Preserve, to adjust the Urban Limit Line by 30 acres to accommodate the development footprint of the project.

Though the Board also separately approved the Tassajara Parks project itself in the summer of 2021, a lawsuit was filed against the project approval, and a subsequent ruling in 2023 vacated that approval pending further analysis of water supply issues.

If and when the Tassajara Parks project is proposed again and approved, it would greatly contribute to the conservation of this region for wildlife, the public, and future generations.

Save Mount Diablo remains unequivocally supportive of the conservation benefits of the 30-acre, 125-unit Tassajara Parks project, including the 17,600+ acre Tassajara Agricultural Preserve, and the protection via dedication of 727 acres of open space that would be achieved once the project is approved.

Although the 727 acres of open space protection would take place in the future if Tassajara Parks is approved again, we are pleased that the Tassajara Valley now and in the future has a double layer of protection: the Urban Limit Line and the agricultural preserve.