Cal. Government Code § 12059

In case of the death, disability, or other failure to take office of both the Governor-elect and the Lieutenant Governor-elect, the last duly elected President pro Tempore of the Senate, or in case of the President pro Tempore’s death, disability, or other failure to take office, the last duly elected Speaker of the Assembly, or in case of the Speaker’s death, disability, or other failure to take office, the Secretary of State-elect, or in case of the Secretary of State-elect’s death, disability, or other failure to take office, the Attorney General-elect, or in case of the Attorney General-elect’s death, disability, or other failure to take office, the Treasurer-elect, or in case of the Treasurer-elect’s death, disability, or other failure to take office, the Controller-elect, or in case of the Controller-elect’s death, disability, or other failure to take office, the Superintendent of Public Instruction-elect, or in case of the Superintendent of Public Instruction-elect’s death, disability, or other failure to take office, the Insurance Commissioner-elect, or in case of the Insurance Commissioner-elect’s death, disability, or other failure to take office, the last duly elected Chair of the Board of Equalization shall act as Governor from the same time and in the same manner as provided for the Governor-elect. The person shall, in the case of death, be Governor for the full term or in the case of disability or other failure to take office shall act as Governor until the disability of the Governor-elect shall cease.