The dusky orange of the Golden Gate Bridge caught all the colors of the rainbow Sunday night, as lights cascaded from it into San Francisco Bay and a soaring pyrotechnic salute rained a glorious shower on the iconic span.

The 18-minute fireworks and light-beam show, partially loosed from the span's 746-foot towers, capped a day of festivities that celebrated the bridge's 75th anniversary.

After milling, cheerful crowds spent the day under sunswept blue skies, they watched as, on a fog-free night, a bowl of still-darkening night captured perfectly a hypnotic display of fiery flowers, parachutes, showers and rockets.

"Oh, my god, I couldn't believe it," said Katherine Hastings, 61, of Santa Rosa, who watched from Crissy Field.

Earlier, the closing sunset lit up the grand old dame of suspension bridges as if she were the star of the stage, which on Sunday, of course, as on so many other days, she was.

"It's a beautiful national landmark and it took so much work and people to build it; it's breathtaking," said Moriah McKiernan-Allen, 23, of Pleasant Hill, who moved to California from Indiana two weeks ago.

The celebration of the bridge's birthday drew at least tens of thousands of people — no crowd estimate was immediately available — to the bridge and the San Francisco waterfront.

"It's a grand creation, and it felt important to be here today," said Benigno Avalos, 37, of Rohnert Park, who brought his family.

Avalos, speaking in Spanish, recalled when he first saw the bridge in 1989 as a teenager, headed north from Mexico into Sonoma County and a new life.

"It was so exciting, because I had only seen in before in books and it was real," he said, resting in the newly built visitors pavilion area at the bridge's south entrance, which includes interactive exhibitions and walking and bicycle trails and opened in May.

Authorities had warned people to refrain from driving into or out of the city Sunday, fearing a traffic nightmare and, while a steady stream of vehicles was on the bridge there were no backups. Also, as opposed to the bridge's 50th anniversary celebration in 1987, when an estimated 800,000 people swarmed the bridge and its approaches, Sunday's events were held over a larger area and the bridge was closed to pedestrians and cyclists.

"What's worked for this is that everything was spread out from Fort Point to Marina Green," said Mary Currie, spokeswoman for the Gold Gate Bridge, Highway and Transportation District.

Bridge district employees had been pressed into a variety of roles during the day that they seemed happy to serve in to facilitate the celebration.

"It's an honor to actually work here," said Brian Vaughn, 46, who usually is assigned to a bridge painting crew but on Sunday was directing traffic.

Just on Saturday night, said Vaughn, though he had worked on the bridge for close to two years already, he was enjoying documentaries about its construction.

"It's awesome knowing that there's a heritage being passed down to us," the former Santa Rosa resident said.

You can reach Staff Writer Jeremy Hay at 521-5212 or jeremy.hay