But supporters of Proposition 8, in what political analysts said was an extremely effective strategy, made the race about much more than that.
They were able to focus the debate on their assertion that without the ban, public school children would be indoctrinated into accepting gay marriage against their parents' wishes, churches would be sanctioned for not performing same-sex weddings and the institution of marriage would be irreparably harmed.
Supporters of gay marriage, along with political leaders including Sen. Dianne Feinstein (D-San Francisco) and the state's superintendent of public instruction, denounced those messages as scare tactics, but they were not able to sway voters. Preliminary returns showed Proposition 8 passing 52% to 48%.
"It was masterful of the campaign to raise the implications of what it could mean in terms of the school system," said Republican political consultant Wayne Johnson. He said voters may have started out "thinking that as long as it doesn't affect me, do what you want" but the supporters shifted the focus to children.
In the wake of the vote, gay couples and their supporters mourned, held rallies, including one in West Hollywood on Wednesday night, filed legal challenges and, in some cases, rushed to the county recorder's office to tie the knot before the state stopped allowing it. The Los Angeles County registrar-recorder stopped issuing same-sex marriage licenses Wednesday afternoon.
At the West Hollywood rally, which drew thousands to San Vicente and Santa Monica boulevards Wednesday night, demonstrators vented their frustrations and cheered when passing cars honked in support. While officers were shutting down streets for the rally, a deputy was accidentally struck by a pickup and suffered minor injuries.
For many demonstrators who had backed Barack Obama for president, Tuesday's elections brought mixed emotions.
"I felt happy and then I felt crushed," said Chris Thurman, 24. He and another friend, 29-year-old T.J. Prokop, carried signs depicting separate straight drinking fountains and gay drinking fountains, a reference to the racially segregated South in the pre-Civil Rights era.
Demonstrator Chris Moll, 35, who was married in October and was carrying his 18-month-old daughter, Ella, in his arms, said the election did not alter his feelings about his marriage.
"Whatever happened last night does not change how I feel about my husband and my family," Moll said. "It is a tough feeling, but I know this is a strong community, and I know we'll find the next step."
Earlier Wednesday, Paul Waters of Valley Village summed up his feelings: "disappointment." "Straight couples don't have a way to be able to truly understand the depth of what this means." Waters married his partner of 15 years, Kevin Voecks, on June 17.
Like them, many gay-rights activists spent the day asking themselves how they had been defeated. At the polls Tuesday, voters throughout the state said proponents' argument about schools was a major part of the answer.
"I'm concerned about having to educate children," Sharon Smith said after she voted in Altadena.
Smith and other African American voters played a crucial role in the outcome. An exit poll of California voters showed that black voters sided in favor of the measure by margins of more than 2 to 1. Not only was the black vote weighted heavily in favor of Proposition 8, but black turnout -- spurred by Barack Obama's campaign for president -- was unusually large, making up roughly 10% of the voters. The exit poll was conducted by Edison Media Research and Mitofsky International for a consortium of news organizations.
The campaign against Proposition 8 also did relatively poorly in Los Angeles County, where voters were divided almost evenly. By contrast, on the other high-profile social issue on the ballot, Proposition 4 on abortion, the liberal side carried Los Angeles by a margin of almost 200,000 votes.
On Wednesday, the proposition's backers celebrated their victory.
"Marriage has been protected," said Cal Schell, 65, a resident of the Sacramento suburb of Rancho Cordova.
Schell said he felt sad that "there's a lot of people who have a lot of angst over this. But it is very important that this be protected. . . . Go to any country, any place in the world. Marriage between a man and a woman has been a part of our being clear back to the days of early time."
Ron Prentice of the Protect Marriage Coalition said in a statement that "the people of California stood up for traditional marriage and reclaimed this great institution. We are gratified that voters chose to protect traditional marriage and to enshrine its importance in the state Constitution."
The campaign against Proposition 8 refused to formally concede Wednesday, saying that there were too many provisional and mail-in ballots to be counted.
The exact number of those ballots remains unclear -- officials said they had no precise count. But a survey by Times reporters of the state's registrars indicated that more than 1.7 million ballots probably remained uncounted. To change the outcome on Proposition 8, the opponents would have to win about two-thirds of those votes, which campaign strategists privately conceded was highly improbable.
In the meantime, gay couples tried to come to terms with what it meant to lose the right to marry.
Susan Allen of Orange, who married her partner, Robin Lambert, on July 11, said she went to the county clerk's office in Santa Ana on Wednesday with the marriage certificate that she had been issued in the summer.
"I said, 'Is this any good?' " Allen said she asked the clerk of the certificate that she had had framed and hung on the wall. The clerk's answer, Allen said, breaking into tears, was that "she was sorry, but she just did not know."
California Atty. Gen. Jerry Brown has said the marriages performed between June 17 and Tuesday will remain valid -- but legal experts expect the marriages to be challenged and say there is no clear answer as to what the courts will decide.
The race -- among the nation's most closely watched ballot campaigns as well as its most expensive -- revealed a deep cultural rift in California.
Many Proposition 8 supporters believed that the future of traditional families was at stake, while opponents were fighting for what they considered the fundamental right of gay people to be treated equally under the law.
The exit poll and a county-by-county review of the results show some major divisions.
As a group, voters under 30 opposed Proposition 8. Whites narrowly opposed it, while Latinos favored it by a small margin.
Opponents of a gay marriage ban drew most of their support along the coastal and wine country communities of the state's northern areas. San Francisco voters, for example, opposed Proposition 8 in droves, with 76.5% voting against the initiative. But those margins were not enough to overcome substantial support for a ban in Southern California and the Central Valley.
In a news conference at San Francisco City Hall on Wednesday, Mayor Gavin Newsom said he would not have done anything differently. Newsom set the constitutional amendment in motion four years ago when he began marrying gay couples, leading to the court case that legalized same-sex unions.
Some political figures have criticized Newsom for pushing the issue too fast. But he rejected that idea.
"I don't regret anything," he said. "I don't regret standing up for people."
He added he was "tremendously optimistic" that California would someday reverse itself on same-sex marriage.
For some voters Tuesday, the decision was not easy.
Jeffrey Jackson of Lynwood said he struggled with how he would vote on Proposition 8. On the one hand, as a black man casting his ballot for Obama, he said he had a deep and personal reverence for civil rights. On the other, he is a Pentecostal Christian.
In the end, it was that religious faith that guided his decision. "It's straight biblical," said Jackson, 46. "It's just not right."