The new Field Poll found that Clinton is currently leading Trump by 58 to 28 percent, The Hill daily reported.
When Libertarian nominee Gary Johnson is factored into the poll, Clinton topped Trump by 24 points, 50 to 26 per cent, with Johnson receiving 14 per cent.
The poll also found that she won the support of 16 per cent Republicans. Trump only got the backing of 5 per cent of Democrats.
Trump told Republican senators on Thursday during a private meeting on Capitol Hill that he would expand the map of battleground states but will not ignore safe Democratic states like California.
The latest installment of the Field Poll was conducted between June 8 and July 2 through telephone interviews in English and Spanish with 956 potential California voters.
The survey has a margin of error of plus/minus 4.4 percentage points.