Demonstrators gather at San Francisco's Civic Center for the Women's March on January 21, 2017, the day after President Donald Trump took office.

Media: Bill Disbrow

All over the Bay Area on Saturday, massive crowds overflowed sidewalks, streets and parks as pro-women, anti-President Trump protesters loudly — and peacefully — declared they will oppose the new administration’s agenda wherever they see it opposing them.

“I have a message for Donald Trump: If you think you can bully women back to the 1950s, think again,” Oakland Mayor Libby Schaaf told a cheering crowd of tens of thousands in front of City Hall, a throng so huge it spilled into nearby streets.

“We will push forward for our generation, for our daughters’ generation, for our granddaughters’ generation, and we will not stop until we have it (women’s equality) written in the United States Constitution,” she said. “We stand up for justice.”

The six Bay Area Women’s March events — “sister marches” to the main one in Washington, D.C. — each demanded attention be paid to the rights of women, minorities, immigrants and the poor, with heaps of performances and singing thrown into the mix.

Organizers said the marches weren’t specifically directed at the new president, who took office just a day before, but an undeniably anti-Trump thread wove through every gathering, along with denunciations of pledges by Trump and the new Congress to cut spending on social services. The protests were peaceful, and by the end of the day there were no skirmishes or arrests reported in the Bay Area.

The Washington march drew hundreds of thousands of people, and there was a huge turnout for similar events in hundreds of cities around the nation and overseas. There were at least 50 marches throughout California.

In San Francisco, the marchers ranged from young to old and included a kaleidoscope of groups, from Planned Parenthood to Black Lives Matter and the National Center for Lesbian Rights. The city’s Women’s March was, coincidentally, on the same day as the Walk for Life, the annual antiabortion march held in the city, but both groups adjusted the timing of their events so that they barely overlapped each other. The goal was to prevent conflict.

That meant San Francisco’s gathering began late in the afternoon, around the time most of the others in the Bay Area were ending. By the time speakers began addressing the crowd around City Hall, which was bathed in pink light, tens of thousands of people were crammed shoulder to shoulder, spreading out several blocks from the plaza. Many wore the pink, cat-eared hats adopted as a symbol by marchers to mock Trump’s comments about women’s private parts.

“Yesterday was for Trump’s rhetoric — today is for fighting back,” Rep. Nancy Pelosi, D-San Francisco, told marchers. “I’m marching today to protect our health care from being torn away from hardworking families.”

Speakers exhorted the protesters to stand together not just for women’s rights, but against Trump’s anti-immigration, anti-LGBT and anti-Islamic rhetoric.

Thousands joined the Women's March in Oakland on January 21, 2017, the day after President Donald Trump took office.

Media: San Francisco Chronicle

“What has brought us together is the reality that all our struggles are the same, and we are stronger together,” Ameena Jandali, content director of the Islamic Networks Group, told the crowd.

Folk singer Joan Baez — a veteran of many protests over the decades — led the crowd in a Spanish rendition of “We Shall Not Be Moved.”

The march made its way down Market Street around 5 p.m. under a heavy downpour. Signs became soggy piles and umbrellas thumped against one another as the long line of marchers headed slowly toward Justin Herman Plaza on the Embarcadero. Even in the rain, spirits remained high, with marchers bursting out with “This Land Is Your Land.”

“I feel like it’s about us standing up for each other and knowing our community is not going to stand idly by,” Rebecca Kidder, 45, of San Francisco said as she held a sign reading “Equal Rights for All Genders.” “We’re going to have our voices heard, so people know we’re not just going to lie down and let this s— happen to us.”

In Oakland, demonstrators gathered early in the morning in Madison Park, holding homemade signs with slogans like “Dump Trump” and “Feminist Dad.” The crowd was so large the park was already overrun before anyone began walking through downtown toward City Hall at Frank Ogawa Plaza.

There was camaraderie among the strangers who had traveled from across the Bay Area — Antioch, Martinez and Danville — as performers sang, drummed and danced alongside the protesters and their picket signs. One person yelled, “Look at all the grannies here!” while others chanted, “Fired up! Ready to go!”

Ann Seitz, a 67-year-old Hayward resident, clutched a sign that said, “Paul Ryan Healthcare Plan: Die already, and hurry up about it.”

“I think the administration right now is really trying to perpetuate a vast theft on the public,” Seitz said. “I also think anybody who is complicit and cooperates with taking away insurance for 20 million people is nothing more than a murderer.”

Samantha Jenny, a 37-year-old Oakland resident, was with her three young daughters, who wore shirts she made for them that read: “Future CEO,” “Future Diplomat” and “Future Engineer.”

“Women are our most underutilized resource in the world, so that’s why I made these shirts,” she said. “These girls will save the world. They’re going to be our future engineers, doctors. I want them to be in a country where their rights matter as much as men.”

Crowds numbering in the thousands also massed in Napa, Walnut Creek, Santa Rosa and San Jose. San Jose Mayor Sam Liccardo tweeted Saturday morning that 25,000 people had come downtown, and the gathering of thousands in Walnut Creek was the biggest in recent memory there.

Long lines of travelers jammed BART stations across the Bay Area, with the trains packed past capacity and occasionally delayed by crowds. The California Highway Patrol closed the Oak Street off-ramp in Oakland for hours because of the huge gatherings and traffic. Streets in downtown Santa Rosa, as in several cities, were blocked off during the march.

The throngs in the suburbs seemed as fired up as those in the cities. In Walnut Creek, men, women and children from throughout the East Bay gathered at Civic Park to hear singers and speakers including state Sens. Nancy Skinner, D-Berkeley, and Steve Glazer, D-Orinda, call for vigilance against any erosion of equal rights. Chanting and waving signs, the crowd began marching through downtown shortly after noon.

“We will not go quietly back to the 1950s,” read one sign. ”Make America kind again,” read another.

“I’m feeling happy that so many people can make it today,” Kylea Clayton, 15, said as she listened to the speakers in Civic Park. “I think everyone in my generation can come together for our rights and get something done.”

Chronicle staff writer Hamed Aleaziz contributed to this report.

Vivian Ho, Kevin Fagan and Sarah Ravani are San Francisco Chronicle staff writers. Email: vho@sfchronicle.com, kfagan@sfchronicle.com, sravani@sfchronicle.com Twitter: @VivianHo, @KevinChron, @SarRavani