In a word, NO, illegal aliens cannot lawfully vote in California, despite rumors to the contrary.
The City of San Francisco, this week, passed an ordinance to allow non-citizens to vote in school elections, contrary to California state law.
The Sacramento Bee, 18 July 2018: Non-citizens legally register to vote in San Francisco school elections
Qualifications to vote in any California local or statewide election are clear and unmistakable. Only US Citizens and legal residents of California may register to vote.
Federal law 18 U.S.C. 611 – VOTING BY ALIENS likewise prohibits noncitizens from voting in federal elections. Cornell Law School provides a convenient summary of the pertinent federal law. This 1996 prescribes penalties – punishment – for aliens (non-citizens), including fines, imprisonment, inadmissibility, and deportation.
Due to conflicting factors, illegal aliens are registering to vote, including voter intimidation laws and motor-voter registration.
Sworn testimony before Congress reports voter fraud in California, Florida, Wisconsin. Many other instances are prosecuted in New York, Virginia, Maryland, Ohio, Utah and here in Texas.