The campaign said Tuesday it has surpassed the required 13,000 signatures, gathering the endorsement of more than 20,000 residents of Solano County, a largely agricultural community located northeast of San Francisco. The initiative, if approved by voters in the county, would pave the way from construction to begin by overturning restrictive zoning laws from the 1980s that limit development outside existing cities.

"That number reflects the breadth and the depth of the support for the east Solano plan across Solano County from people from all walks of life, all parts of the county," said Jan Sramek, a former Goldman Sachs Group Inc. trader who is the founder and chief executive officer of the company behind the project, California Forever. 

The proposed ballot measure includes zoning changes to allow for the development of 17,500 acres for the new city, which is expected to house 50,000 residents. 

With backers including former Sequoia Capital Chairman Michael Moritz and social-impact investor Laurene Powell Jobs, Sramek and his team say they're on mission to ease California's housing crisis and restore the era of walkable downtowns that was lost to the rise of suburbs and American car culture.

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Tuesday's announcement at an event in Vallejo marks a significant milestone for a campaign that's been marred by controversy from the start. Since first revealed to the public, the secretive project has faced fierce criticism from locals, farmers and politicians who have accused Sramek and his supporters of using intimidation tactics to acquire the land needed to construct the development.