(CNN) California Sen. Kamala Harris, former Vice President Joe Biden and Vermont Sen. Bernie Sanders are in a close race in California, according to a new Quinnipiac poll released Wednesday.

The poll shows Harris at 23%, Biden at 21% and Sanders at 18%. The difference between the candidates' numbers are within the poll's margin of error.

Beyond the top three, Massachusetts Sen. Elizabeth Warren sits at 16%.

The race has tightened since a Quinnipiac April survey found Biden, who had not yet formally announced his candidacy, besting the other contenders with 26% of Democratic voters in the Golden State; in that poll, Sanders was at 18%, Harris 17% and Warren 7%.

Harris and Warren have both surged since that survey, while Biden has dropped and Sanders has remained steady.

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