The bride wore a pastel-coloured pant-suit – and so did the other bride. At 5.01pm yesterday, Phyllis Lyon and Del Martin walked up the steps of San Francisco's City Hall and the two women became the first gay couple to take advantage of California's decision to legalise same-sex marriage.

After half a century together, the couple, who are both in their eighties, were married in front of 50 guests by the city's mayor, Gavin Newsom. They were hand-picked to usher in a "summer of love" in recognition of their status as pioneers of the gay rights movement.

When Ms Lyon, 84, and Ms Martin, 87, fell in love in 1952, gays and lesbians faced arrest and imprisonment; in some cases, they were subjected to electro-shock therapy. This week, after a long campaign, thousands are rushing to celebrate equality – of a sort.

"It's something that's been due a long time, so thank God it's finally here," Ms Lyon told reporters. "Our love and lives together deserve celebrating. Although we have little need for more kitchen gadgets, we do believe a government acknowledgment of our fundamental constitutional rights is a fitting gift."

The couple's wedding was one of two commemorative ceremonies organised to mark the onset of a Supreme Court ruling that same-sex couples have identical marital rights to their heterosexual counterparts. Marriage licences will be issued to other gay and lesbian couples from 9am today. Although the new law may be short-lived – it faces a public vote in November – tens of thousands of couples from across America are expected to take advantage of the window of opportunity, and formalise their union in the next few months.

A study by UCLA predicts that half of California's 102,639 gay couples are planning to marry, with around 68,000 coming in from elsewhere in the US. The research, by the university's Williams Institute, values the economic proceeds of the "summer of love" at $684m (£350m), including $64m in tax revenue.

The new laws make California the only place in the US to permit universal same-sex weddings, although Massachusetts has for several years allowed residents to enter civil partnerships. With the average US wedding costing $30,000, cake manufacturers, florists, hotels, and firms such as myqueerwedding.com are already cashing in.

"This is a multibillion-dollar business and [gays and lesbians] are virtually shut out from it," said Donna Hoffman, a marketing professor at the University of California. "We can expect a lot of weddings, and these people need to be served commercially. This is a huge opportunity."

Celebrations come with a note of caution, however. In November, voters are expected to approve a constitutional amendment proposed by religious groups legally to define marriage as a union between a man and a woman – thereby ending the flood of weddings that begins today. The issue may influence the presidential race. Barack Obama is calling for the repeal of the Defence of Marriage Act, which prohibits federal government from recognising gay weddings. John McCain supports the Act, and will give individual states the right to "ban" gay marriage.