(taken from here - https://ocvote.gov/election-library/docs/vacancy.pdf)
(snip)
VACANCIES IN THE OFFICES OF
REPRESENTATIVE IN CONGRESS, STATE SENATOR, AND
STATE ASSEMBLY MEMBER
GOVERNORS PROCLAMATION
The Governor shall call a statewide special election by issuing a proclamation pursuant
to Elections Code Section 12000 in the event of a vacancy in the office of
Representative in Congress (congressional), State Senator (legislative), or Member of
the State Assembly (legislative).
In the case of a vacancy in a congressional or legislative office, the Governor shall issue
a writ of election, within 14 calendar days of the occurrence of the vacancy, calling a
special election to fill the vacancy in accordance with Elections Code Section 10703. A
copy of the proclamation shall be sent to the board of supervisors of every affected
county.
California Constitution, Article IV, Section 2(d), Government Code § 1773,
Elections Code § 10700
Vacancies Occurring After the Close of Nomination:
When a vacancy occurs in a congressional office after the close of the nomination
period in the final year of the term of office, the Governor may decline to issue an
election proclamation at his discretion.
Elections Code § 10701(a), Government Code § 1773
When a vacancy occurs in a legislative office after the close of the nomination period in
the final year of the term of office, no special election shall be held.
Elections Code § 10701(b), Government Code § 1773
SPECIAL ELECTION
Calling the Election:
A special election to fill a vacancy in the office of Representative in Congress, State
Senator, or Member of the Assembly shall be conducted on a Tuesday at least 126
days, but not more than 140 days, following the issuance of an election proclamation
by the Governor pursuant to Section 1773 of the Government Code.
However, the special general election may be conducted within 180 days following the
proclamation in order that the election or the primary election be consolidated with the
next regularly-scheduled statewide election or local election occurring wholly or partially
within the same territory in which the vacancy exists, provided that the voters eligible to
vote in the local election comprise at least 50 percent of all the voters eligible to vote on
the vacancy. (See Exhibit B for established election dates and Exhibit D regarding
consolidation with another election)
Elections Code § 10703(a)
(snip)
Will have to see how Newsom handles this!