At least five county clerks around the state extended their hours to issue marriage licenses, and many same-sex couples got married on the spot.
"These are not folks who just met each other last week and said, `Let's get married.' These are folks who have been together in some cases for decades," said Kate Kendell, executive director of the National Center for Lesbian Rights. "They are married in their hearts and minds, but they have never been able to have that experience of community and common humanity."
The really big rush to the altar in the nation's most populous state was not expected to take place until Tuesday, which is when most counties planned to start issuing marriage licenses to gay couples. Hundreds, perhaps thousands, of couples from around the country are expected to seize the opportunity to make their unions official in the eyes of the law.
More than 1 million Californians signed an amendment to ban same-sex marriage, but between now and then, the state is bracing for a rush to wed, CBS News correspondent John Blackstone reports.
Local officials are now required to issue licenses that have the words "Party A" and "Party B" where "bride" and "groom" used to be.
In San Francisco, Mayor Gavin Newsom, who helped launch the series of lawsuits that led the court to strike down California's one-man-one-woman marriage laws, presided at the wedding of lesbian rights activists Del Martin, 87, and Phyllis Lyon, 84.
Well-wishers cheered when they emerged outside Newsom's office after the ceremony.
Dozens of couples gathered outside the clerks offices in Alameda, Sonoma and Yolo counties, where hours were extended to accommodate gay couples who wanted to be among the first to marry.
Derek Norman, 23 and Robert Blaudow, 39, from Memphis, were in the Bay Area for a conference and decided to get married at the Alameda County clerk's office.
"We might wait a long time in Tennessee, so this is our chance," Blaudow said.
First in line to pick up a marriage license in Sonoma was Melanie Phoenix, 47, and Terry Robinson, 48, of Santa Rosa. They have been together for almost 26 years and plan to be wed in August.
"It's an historic occassion," Phoenix said. "I never believed it was really possible until Gavin Newsom took the first step in 2004."
A throng of well-wishers and news media surrounded a lesbian couple as they were married in a Jewish ceremony in front of the Beverly Hills courthouse.
The ceremony was broadcast live on three newscasts in Los Angeles.
The couple wept and pressed their foreheads together, and onlookers whooped as the marriage became valid.