Cal. Educ. Code § 23106

If a member ceases to be entitled to credit for service in the Defined Benefit Program because the member has become entitled to credit for that service in another retirement system supported wholly or in part by funds of the United States government, or any state government or political subdivision thereof, the member is entitled to a refund of the accumulated retirement contributions made during the period for which he or she is entitled to credit in the other retirement system.