Marriage equality advocates celebrated on the step of City Hall after it was announce that U.S. District Court Judge Vaughn Walker struck down the voter-approved same-sex marriage ban yesterday.

Walker said in a 136-page decision that the measure violated the U.S. Constitution’s guarantees of due process and equal treatment, adding that “California’s obligation is to treat its citizens equally.”

Defenders of the 2008 initiative presented just two witnesses, who according to Judge Vaughn Walker, were unqualified experts. Neither  witness could offer any credible evidence that gay marriage harms heterosexual marriage or that barring gays from marrying promotes any legitimate state interest.

During a cross examination, one the defense’s witnesses, Prop 8 supporter and president of the Institute for American Values, David Blankenhorn conceded under cross-examination that he believed allowing gays to marry would be beneficial to the couples and their children. “We would be more American on the day we permitted same-sex marriage than we were the day before.”

A notice of appeal was filed minutes after Walker’s ruling, but the Prop. 8 case will likely not be held until early 2011, according to a briefing schedule posted by a federal appeals court in San Francisco Thursday.