Save Mount Diablo Supports Key Open Space Protection Tool
In a win for open space protection, in early December the Contra Costa County Board of Supervisors approved sending a measure to renew the county Urban Limit Line to the June 2026 ballot.
Save Mount Diablo was involved throughout the process of drafting the line to ensure it protected open space and did not make development easier in areas that should be protected.
We look forward to helping this key land protection measure win at the ballot box.
The Urban Limit Line protects thousands of acres from development in the Diablo Range. Photo: Scott Hein
What Is an Urban Limit Line?
An Urban Limit Line is a line that an agency adopts beyond which “urban-style” development, like an industrial area or large residential subdivision, cannot occur.
It’s a crucial land use tool that protects open space outside of the line and helps focus development inside the line.
Open space and agricultural activities can still occur outside the line, including some house building, such as a house on a land parcel zoned as agriculture (the idea being, the landowner or workers reside on the land).
Cities and counties can adopt Urban Limit Lines to limit outward growth and help focus resources toward areas that are already built up, where infrastructure and services already exist.
Contra Costa County has the goal of limiting urban land-use designations to 35 percent of the county, leaving the rest of the land designated for things like agriculture and open space. The Urban Limit Line is key to maintaining that 65-to-35 balance.
Each city in the county has its own Urban Limit Line, so the renewal doesn’t affect them. It’s specifically for county development, not cities like Concord, Antioch, and others.
The Urban Limit Line can be adjusted by 30 acres with a four-fifths vote of the county Board of Supervisors if certain findings, like overwhelming public benefit, are met.
Bigger changes would require approval by county voters. The Urban Limit Line has only been changed a very few times since it has been created, and only once for development. It’s done a great job of defending open space!
The Urban Limit Line is key to maintaining Contra Costa County’s 65 percent balance for open space. Photo: Stephen Joseph
Why Does the Urban Limit Line Need to be Renewed?
Contra Costa County voters initially approved the Urban Limit Line in 1990.
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 Urban Limit Lines.
Voters approved the Urban Limit Line again in 2006 by passing Measure L, which extended the life of the Urban Limit Line by 20 years. After 20 years, voters could decide on whether to renew it or not.
An agency that wants to receive local street maintenance funds needs to have an adopted Urban Limit Line.
For Contra Costa County, these funds sum to about $2 million a year. To receive the funds, the county needs to have an adopted Urban Limit Line.
Open space protected by the Contra Costa Urban Limit Line. Photo: Scott Hein
What’s Save Mount Diablo’s Role?
Save Mount Diablo has been one of the strongest supporters of the creation and defense of Urban Limit Lines in Contra Costa County.
We knew that as we got closer to 2026, the Urban Limit Line would need to be renewed. County staff worked with us and other stakeholders to get our feedback on the proposed new line.
We didn’t want developers that had pet projects on the edge of the current line to get a new expanded Urban Limit Line that would include their projects.
As a result, the new line is even better than the one it is replacing. It’s being tightened by about 11,100 acres all around the county.
It will exclude (move outside of the line compared to the old line) areas that restrict development (such as conservation easements or parks). It adds development constraints for areas that are very steep or high fire hazard severity zones.
It expands the current Urban Limit Line by just 1,600 acres to adjust for development that already exists, current city limits, and other things. The changes make sense and don’t threaten open space.
Contra Costa County’s Urban Limit Line has been an important tool in protecting the agriculture and open space of the county and incentivizing development in appropriate areas since it was created.
Given the intensifying impacts of climate change and the disastrous results of sprawl, land use policies that encourage compact and efficient infill development, such as the Urban Limit Line, are more essential than ever.
If Contra Costa County is to protect its natural resources, improve development, and increase resilience in the face of a more extreme climate, it is vital that the Urban Limit Line is renewed.
Save Mount Diablo looks forward to supporting the Urban Limit Line renewal in 2026 as it goes to the ballot box.
Urban Limit Lines keep precious open space from being developed. Photo: Scott Hein
