A campaign committee, Yes California Independence Committee, has been around for at least two years, but the election of President Donald Trump only saw increased momentum for the so-called Calexit cause, Los Angeles Times reported.
He lost California by more than 4 million votes, fuelling interest in a Calexit - a play on the UK's "Brexit" campaign that saw Britain's voters decide to leave the European Union.
The group needs 585,407 signatures from registered voters over the next 180 days to qualify for the ballot.
"If the 2018 ballot initiative passes, it would force a 2019 statewide special election asking voters if they want California to become an independent country," it said.
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If at least half of registered voters participate in that vote, with at least 55 per cent of those voting to approve, the results would be treated as California's declaration of independence, the paper said.
"California loses [by] being a part of America culturally and financially," said Marcus Ruiz Evans, one of the campaign's founders. "It could be a nation all its own, everybody knows that. The only question is if they want to break off."
Supporters first proposed a ballot measure to the state attorney general's office in November.
According to a summary prepared by the state attorney general, if the measure got onto the ballot and passed, it would repeal clauses in the California Constitution stating that the state is an "inseparable part of the United States" and that the US Constitution is the "supreme law of the land," the Los Angeles Times reported.
It's not clear whether a California secession would be handled by the federal government, even if the state's voters approved it.