SAN FRANCISCO -- Thousands of anti-abortion protesters from across California marched through downtown San Francisco on Saturday to mark the 41st anniversary of the landmark Supreme Court ruling that legalized the procedure.

A massive and diverse crowd of protesters rallied in front of City Hall before marching down Market Street to Justin Herman Plaza for the 10th annual Walk for Life West Coast. They chanted "pro-life!" and carried signs that read "Defend Life" and "Women Deserve Better Than Abortion."

San Francisco police did not immediately provide an official crowd estimate, but at one point marchers stretched along more than a mile of Market Street.

Nancy Castellanos, a 17-year-old high school senior from Dixon, came to San Francisco with worshipers from St. Peter's Catholic Church, which brought people on six buses. She believes the laws need to change to make it harder to get an abortion.

"I am 100 percent, completely against abortion," she said. "If you don't want the child, there's always adoption."

John Paine, 52, arrived with people from his church group in the Central Valley city of Visalia.

"I'm ashamed that my country sanctions the killing of its most defenseless of its citizens," he said. "Human life in all its stages is sacred and should be protected."

Last week, San Francisco Supervisor David Campos introduced a resolution opposing the "Abortion Hurts Women" banners that protest organizers hung on Market Street.

On Wednesday, thousands of anti-abortion activists participated in the annual Walk for Life rally in Washington, D.C., to mark the 41st anniversary of Roe v. Wade, the 1973 Supreme Court decision that legalized abortion.

A small group of abortion-rights activists protested the march on Market Street, holding signs that read "Abortion on Demand and Without Apology."

Anna Wilson, 20, a commercial artist who lives in San Francisco, said she participated in the Walk for Life march two years ago but said she's since changed her stance on abortion.

"I realized I was looking at it in a real childish way," Wilson said. "I'm not pro-abortion. Nobody's pro-abortion. But I am pro-choice. I think that women should have every single choice available to them, as much as men do."

Over the past several decades, anti-abortion groups have focused on placing relatively small restrictions on abortion, especially in conservative states with Republican-dominated legislatures. Lawmakers in those states are under increasing pressure from activists to take stronger action to limit abortion.

But California, which has a Democratic governor and Legislature, expanded abortion access last year with a measure that allows nurse practitioners, certified nurse midwives and physician assistants to perform a type of early abortion.