Demonstrators outside the court booed, wept and yelled, "Shame on you!" Some gay activists blocked a busy intersection in San Francisco in protest and others are already preparing for another battle at the polls, reports CBS News correspondent John Blackstone. The issue could be before California voters again as early as next year.
In a 6-1 decision written by Chief Justice Ron George, the court rejected arguments that the ban approved by the voters last fall was such a fundamental change in the California Constitution that it first needed the Legislature's approval.
As for the thousands of couples who tied the knot last year in the five months that gay marriage was legal in California, the court said it is well-established principle that an amendment is not retroactive unless it is clear that the voters intended it to be, and that was not the case with Proposition 8.
Moreover, the court said it would be too disruptive to apply Proposition 8 retroactively and dissolve all gay marriages.
Doing that would have the effect of "throwing property rights into disarray, destroying the legal interests and expectations of thousands of couples and their families, and potentially undermining the ability of citizens to plan their lives according to the law as it has been determined by this state's highest court," the ruling said.
While gay rights advocates accused the court of failing to protect a minority group from the will of the majority, the justices said that the state's governing framework gives voters almost unfettered ability to change the California Constitution.
The decision set off an outcry among a sea of demonstrators who had gathered in front of the San Francisco courthouse, holding signs and waving rainbow flags. Many people also held hands in a chain around an intersection in an act of protest.
"We're relieved our marriage was not invalidated, but this is a hollow victory because there are so many that are not allowed to marry those they love," said Amber Weiss, 32, who was in the crowd at City Hall, near the courthouse, with her partner, Sharon Papo. They were married on the first day gay marriage was legal last year, June 17.
"I feel very uncomfortable being in a special class of citizens," Papo said.
Jeanne Rizzo, 62, who was one of the plaintiffs along with her wife, Pali Cooper, said: "It's not about whether we get to stay married. Our fight is far from over. I have about 20 years left on this earth, and I'm going to continue to fight for equality every day."
Opponents of same-sex marriage say the California Supreme Court properly respected the will of the people, reports Blackstone.
"The battle is over," said Howard Garber of the American Civil Responsibilities Union. "The fight on this issue has been settled."
A small group of Proposition 8 supporters gathered outside the court.
"A lot of people just assume we're religious nuts. We're not. But we are Christians and we believe in the Bible," said George Popko, 22, a student at American River College in Sacramento, where the student government officially endorsed Proposition 8.
In the state capital, Republican state Assemblyman Sam Blakeslee of San Luis Obispo, the incoming minority leader, said the court's decision "reaffirmed the principle that the people's votes do matter."
The state Supreme Court ruled 4-3 last May that it was unconstitutional to deny gay couples the right to wed. For a while, that put California - the nation's most populous state - back in its familiar position in the vanguard of social change; at the time, Massachusetts was the only other state to allow gay marriage.
In what gay activists called their "Summer of Love," same-sex couples from around the country rushed to get married in California for fear the voters would take away the right at the ballot box. In November, Proposition 8 passed with 52 percent approval.
Over the past several months, as the fight went on in California, Iowa, Maine, Vermont and Connecticut legalized gay marriage, bringing to five the number of states that allow same-sex couples to wed.
In California, gay rights activists argued that the ban was improperly put to the voters and amounted to a revision - which required legislative approval - not an amendment. But the justices disagreed.
The court said that while the ban denies gay couples use of the term "marriage," it does not fundamentally disturb their basic right to "establish an officially recognized and protected family relationship with the person of one's choice and to raise children within the family." California still allows gay couples to form domestic partnerships.
In their 136-page majority ruling, the justices said it not their job to address whether the ban is wise public policy, but to decide whether it is constitutionally valid, while "setting aside our own personal beliefs and values."
"No surprise here," said CBS News legal analyst Andrew Cohen. "It's a ruling that tracked the oral argument in the case where the Justices expressed concern about overturning Prop 8 as the expression of majority rule but also expressed support for existing same-sex marriages."
Cohen said the court's decision to allow existing same-sex marriages to continue means that there will not be two classes of same-sex unions in California. "That might prompt some sort of equal protection challenge down the road," he said.
Justice Carlos Moreno, who had been under consideration as President Barack Obama's nominee to the U.S. Supreme Court, was the lone dissenter.
He said denying same-sex couples the right to wed "strikes at the core of the promise of equality that underlies our California Constitution." He said it represents a "drastic and far-reaching change."
"Promising equal treatment to some is fundamentally different from promising equal treatment for all," Moreno said. "Promising treatment that is almost equal is fundamentally different from ensuring truly equal treatment."
San Francisco City Attorney Dennis Herrera, whose office fought the ban, said: "Today we are faced with a disappointing decision. But I think we also know it could have been worse."
Democratic state Sen. Christine Kehoe of San Diego said that California "has lost its lead in the fight for civil rights for all people." And Assemblyman Tom Ammiano of San Francisco warned the ruling would create "apartheid" in California.