The survey, which was conducted Sept. 16-25, finds 23% of likely voters now backing Warren, 22% supporting Biden and 21% favoring Sanders. The poll puts Harris at 8% and South Bend, Indiana, Mayor Pete Buttigieg at 6%.
But PPIC President Mark Baldassare said the race is still too fluid to make any solid determinations.
"First of all, I think there are three front-runners and, secondly, I think that the election is up for grabs," he said. He noted that while only 9% of respondents consider themselves undecided, more than half of the state's likely Democratic voters said they remain open to supporting a different candidate.
"Many voters in our poll said they are closely following the election, that the debates are very important and that they are not firm in their support for the candidates," Baldassare added.
The survey tracks closely with two other recent public opinion polls: A KQED/Change Research poll released after the third presidential debate in September and the UC Berkeley Institute of Governmental Studies poll released last week. All three polls have Warren ahead of her Democratic rivals, but only by single digits. And since California allocates its 495 delegates proportionally (as opposed to a winner-take-all system), the massive state could be useful to more than one candidate come the March 3 primary.
The poll also indicates that voters are paying close attention to debates: A solid 84% said that candidate performances on the debate stage influence their voting decisions.
The survey of 1,705 adults was taken by phone, with a margin of error of plus or minus 3.2%.
Much like Warren's performance nationally, Baldassare said, this most recent state poll indicates that she has been most successful in growing her base of support in recent months, as compared to Sanders and Biden, who have "their base and many of those people have stuck with them, but they haven't grown their support."
But he also noted that Biden and Sanders have been the two candidates most seriously tested so far on the debate stage and in public interviews. Now, he said, "it will be Warren's turn."
The poll was conducted as revelations over President Trump's July call with Ukranian President Volodymyr Zelensky continued to seep out, meaning that some respondents were unaware of all the week's impeachment-related news.
But Baldassare said he didn't notice any marked change among those surveyed later in the week. And more broadly, he added, the poll doesn't show any meaningful shift in Californians' opinions of Trump, which remain firmly tied to partisan leanings: 90% of Democrats said they disapproved of how the president is doing his job, while the same percentage of Republicans felt the opposite. Independents were slightly less lopsided, with nearly two-thirds disapproving of Trump's performance and about one-third approving.
"A poll is a snapshot in time, and what a time," Baldassare said. He noted, however, that opinions of the president among Californians haven't noticeably changed since Trump was elected. "Everybody has made up their minds."
The PPIC poll did, however, find one area where Californians' minds have changed significantly. When asked about the most pressing issue the state currently faces, homelessness was cited most frequently, with 15% of respondents referring to it as the biggest problem. Among respondents from Los Angeles and the Bay Area, nearly 25% named it their number one concern.