This Los Angeles Times article says four Democrats who are running for California Lieutenant Governor have raised at least $600,000 in campaign funds, and a fifth who might seek that office has raised $2.8 million. It also says, “So far, no major Republican candidates are actively campaigning for Lieutenant Governor.”
Under the top-two system that has been in effect in California since 2011, this probably means that the only two choices on the November 2018 ballot for Lieutenant Governor will be two Democrats. No write-ins will be permitted.
California elections for Lieutenant Governor are separate from gubernatorial elections. The only other populous state that has separate elections for Governor and Lieutenant Governor is Texas.