Obama's approval ratings in the Golden State dropped to just 45 percent, a Field Poll released Tuesday found.
That number is down 5 points from June and dips below 50 percent for the first time in nearly three years. Disapproval, meanwhile, hit 43 percent.
Mark DiCamillo, the director of the Field Poll, said the trend is particularly bad for the president because the declines came from his base.
"These are constituencies that have been strong followers," DiCamillo said, adding that they feel "frustration in the president not getting his way in affecting policy in Washington."
DiCamillo said the findings should have California Democrats concerned about November, where Obama's unpopularity may drag down vulnerable Democrats running for congressional seats, as "the opinions of likely voters in November are even more negative" than the state as a whole.
The Real Clear Politics average finds Obama's approval rating upside-down nationally, with 52 percent disapproving of his performance and 42 percent approving.
Obama won California by more than 23 points in 2012, getting 60 percent of the vote to Mitt Romney's 37 percent. Nationally, he won 51 percent of the popular vote over Romney's 47 percent.