The Seattle area’s premier homebuilders group spent big in last week’s election in Black Diamond but didn’t get much return on its investment.

All four candidates backed by the Master Builders Association of King and Snohomish Counties lost big-time.

The homebuilder-backed mayor, Rebecca Olness, received only 30 percent of the vote.

The most successful of Olness’ three pro-growth allies running for City Council won a paltry 34 percent; the least successful didn’t quite hit 24 percent.

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The $9,995 spent by the Master Builders in the unsuccessful attempt to influence 2,752 voters reflects the high stakes in a battle over development.

At the center of that battle are two planned communities that could bring 6,000 new homes and a million square feet of commercial space to the 4,170-resident city on the far edge of King County’s urban-growth area.

Brian Ross, CEO of YarrowBay, the developer of those urban villages, is also president of the Master Builders.

A Master Builders official said Ross played only a minor role in the decision to pour so much money into the Black Diamond elections.

The Master Builders’ political committee, the Affordable Housing Council, seeks to elect “pro-housing candidates” in two counties, said David Hoffman, the group’s PAC coordinator and King County government-affairs manager.

Since the City Council approved YarrowBay’s urban villages in 2010, voters have thrown out every elected official who supported that decision.

A citizens’ challenge to the projects is pending before the state Court of Appeals.

Mayor-elect Dave Gordon clobbered Olness with 69 percent of the vote.

A mailer accused Gordon of planning to take the city into bankruptcy ­— and said that his plan likely would mean selling off Lake Sawyer Regional Park for a water slide and amusement park. The mailer was funded by Neighbors for a Better Black Diamond, which received most of its money from the Master Builders.

Gordon, a Boeing systems administrator, said he’s never advocated bankruptcy. The ad, he said, was part of “a huge smear campaign” and “a cruel attempt by the mayor to discredit my campaign.”

The smears, he said, “just blew up in their face.”

Gordon said he believes he was attacked so fiercely because he opposes creation of the state’s first community facilities district, which YarrowBay says would accelerate construction of roads, a fire station and utilities, but which Gordon says would put taxpayers at risk.

Olness said she “heard from several people” that Gordon suggested bankrupting the city so it could nullify its development agreements with YarrowBay.

If voters think the election will stop the urban villages, Olness said, they’ll be surprised. “They think, ‘Yeah, we can stop it.’ That just can’t be done,” she said.

The Master Builders’ Hoffman said he hasn’t met Gordon and wasn’t involved in writing the attack ad.

Hoffman said the entire Affordable Housing Council — not Ross, who is one member — made the decision to spend heavily on the Black Diamond elections.

“It was a unanimous decision,” Hoffman said. “All 21 members agreed this was the right move after a lot of debate and discussion over whether or not it was politically, and for our limited finances, the right move for us. …

“We viewed that slate of candidates as the slate that supports housing in Black Diamond.”

Keith Ervin: 206-464-2105 or