President Joe Biden is expected to appear in Long Beach on Monday to help the governor keep his job in Tuesday's election.
Newsom appeared at a rally in Sun Valley with U.S. Sen. Alex Padilla, whom the governor appointed to his post when Kamala Harris was elected vice president.
Newsom urged the crowd not to take the election for granted, and he blasted Elder for his views on multiple issues.
"Doesn't believe in a minimum wage at all," Newsom said. "Doesn't believe there should be any corporate tax. Doesn't believe in an assault weapons ban."
Elder held his own news conference in the Los Angeles area, alongside actress and activist Rose McGowan who is supporting his campaign.
"This man, Gavin Newsom, has been able to switch this thing from a referendum on his behavior, his governance, into a quote 'Republican takeover,'" Elder said. "As if that has anything to do with crime. As if that has anything to do with homelessness. As if that has anything to do with the cost of living."
Early voting underway throughout SoCal
Voting has already been underway, both via mail-in ballots and at early voting centers. Some counties, like Los Angeles, report more than a third of the ballots had been turned in by last week.
Hundreds of early voting centers and dropoff sites were open this weekend and on Monday. In Riverside County alone, there are 144 early-voting locations open.
George Deschryver of Riverside rode up to his local voting center on a motorcycle and didn't even have to turn off the engine to drop off his ballot.
"I want my voice to be heard," Deschryver said. "I live here, it affects my family, my life. I just want to make sure that I always vote."
Other voters preferred to cast their ballots in the traditional way - filling them out in a booth rather than mailing them in - even if they were casting the vote on a non-traditional early day.
"It was important for me to see that I am physically putting it into a box here at the official location, at the registrar of voters, instead of just some random box down the street from my house," said one woman casting her vote in Riverside.
Polls will be open on election day 7 a.m. to 8 p.m. Voters who are already in line when polls close will be allowed to cast their votes.