Government Code § 31509
ARTICLE 2. Establishment of System
A member who has made special contributions to a superseded system shall have the option of withdrawing such special contributions together with interest thereon, following the transfer of contributions to this system, or of permitting the contributions to remain as additional contributions to this system. Any member electing to make such withdrawal shall do so by written notice addressed to the board within 90 days after the effective date of this system.