With the historic trial of a challenge to California's gay marriage ban nearing the end of its first week, two more experts testified Thursday on the negative fallout of denying same-sex couples the right to wed, from costing a local government such as San Francisco's millions of dollars a year to the mental health toll on gays and lesbians across the state.

SAN FRANCISCO — With the historic trial of a challenge to California's gay marriage ban nearing the end of its first week, two more experts testified Thursday on the negative fallout of denying same-sex couples the right to wed, from costing a local government such as San Francisco's millions of dollars a year to the mental health toll on gays and lesbians across the state.

The Proposition 8 trial resumes Friday morning with the likelihood of a day with a few more fireworks than Thursday's expert-laden testimony.

Lawyers for same-sex couples challenging the gay marriage ban plan to call William Tam, a controversial proponent in the Proposition 8 movement, to the witness stand to grill him on the highly-charged 2008 campaign to pass the law, a key ingredient in the effort to prove the measure was infused with a discriminatory intent that violates the federal constitution.

Helen Zia, a San Francisco writer and lesbian, also is expected to testify on the importance of marriage to same-sex couples, having married her partner in 2008 before the initiative went into effect.

The evidence is being presented on the plaintiffs' side in a legal challenge to Proposition 8, the voter-approved law restoring California's ban on same-sex marriage. Chief U.S. District Judge Vaughn Walker is holding the trial, the first of its kind in the nation's federal courts, to consider the claims of same-sex couples that the initiative violates their federal equal protection rights.

Thursday, Ilan Meyer, a Columbia University professor, testified on his research into the mental health damage caused to gays and lesbians by discrimination and the denial of marriage rights. Proposition 8 lawyers tried to discredit Meyer's theories, depicting him as a supporter of gay marriage who contributed to the campaign to defeat the marriage ban, but the professor insisted such laws dramatically raise the stress in the lives of gays and lesbians.

"It doesn't add up to a very welcoming environment," he testified.

Same-sex marriage advocates also put on an expert to show that denying marriage rights to gays and lesbians carries economic costs for local governments in the state. Edmund Egan, the city and county of San Francisco's chief economist, testified it costs the local government's coffers as much as $35 million a year in lost revenue from weddings, hotels, and related expenses by denying gay and lesbians the right to marry in the city.

In addition, Egan said data shows costs to public health budgets from Proposition 8.

Egan conceded it is difficult to attach firm numbers to some of his projections, which Proposition 8 lawyers used to try to show his testimony was imprecise and speculative.

David Boies, one of the lead lawyers for the couples, told Walker that the plaintiffs expect to rest their case by the end of the day Wednesday.

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