The protesters rallied against the approval of Proposition 8, which banned same-sex marriage in California on Tuesday.
"I believe with my heart that the movement of history is on our side," said University of Redlands chaplain John Walsh during a speech comparing the fight for gay rights to the fight to end racial segregation.
"I was told that this was God's will," he said of segregation.
Citing a refrain from the Obama campaign, the protesters shouted "Yes, we can," before traversing much of downtown.
Sunday's protest was just one of many No on 8 rallies held throughout the state since the marriage ban passed. Until that time, same-sex marriage was legal following a May ruling by the California Supreme Court.
During another day of protests in California on Sunday, Gov. Arnold Schwarzenegger called the passage of Proposition 8 "unfortunate" on CNN.
"But it is not the end because I think this will go back into the courts. ... It's the same as in the 1948 case when blacks and whites were not allowed to marry; this falls into the same category."
Passers-by greeted the enthusiastic crowd in Redlands by honking their horns and showing support, though others also expressed their First Amendment rights by yelling or flashing obscenities at the crowd.
Many of the marchers said they were depressed with the results of Tuesday's election.
"I think it's fair that everybody should have equal rights," said 53-year-old San Bernardino resident Janet Wilson, who came with her spouse Rose Sanchez, 57. Sanchez and Wilson have been together 17 years and were married Nov. 1.
"I was angry, hurt," Wilson said of her reaction to Tuesday's results.
The protesters chanted and waved signs and rainbow flags while marching.
"Gay, straight, black or white, marriage is a civil right," they said in unison in front of City Hall.
Jenna Sant, 20, a student at UC Irvine who grew up in Redlands, said Tuesday's vote marks a return to "separate but equal."
"It's not a moral issue. It's a civil rights issue," she said.
University of Redlands student Nick Zaharopoulos, 20, said he went to bed Tuesday night crossing his fingers that Proposition 8 would fail but said he is now hopeful challenges to the proposition will succeed.
"I still have faith that California's going to do the right thing," he said.
The Associated Press contributed to this report