California Code, Government Code - GOV § 1773

When a vacancy occurs in the office of Representative to Congress, or in either house of the Legislature, the Governor shall within 14 calendar days after the occurrence of the vacancy issue a writ of election to fill the vacancy; provided, that when such vacancy occurs in a congressional office after the close of the nomination period in the final year of the term of office, a special election may be held, at the Governor's discretion; and provided, further, that 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.

The Governor shall issue the election proclamation under his hand and the Great Seal of the state, and transmit copies to the board of supervisors of the counties in which the election is to be held.