Cal. INS § 1193

Excess funds investments may be made in bonds of any permanent road division, or any district of any state when such bonds are legal investments for savings banks of this State, or have been certified as legal investments for savings banks pursuant to Division 10 of the Water Code, or when the statutes or laws providing for the issuance of such bonds, provide that such bonds shall be entitled to the same force or value or use as bonds issued by any municipality, or such law specifically states that such bonds shall be legal investments for either savings banks, insurance companies, all trust funds, state school funds or any funds which may be invested in bonds of cities, counties, cities and counties, school districts, or municipalities in the State, or when such bonds have been investigated and approved by a commission or board now or hereafter authorized by law to conduct such investigation and give such approval when such law specifies that upon such approval said bonds are legal investments for insurers, or which the commissioner approves in writing as legal for investment of the funds of insurers. The commissioner in determining whether to approve any bonds as legal investments which do not otherwise qualify as such, shall make, upon the request of any insurer, at such insurer’s expense, an investigation and finding as provided for in Section 1175.