Review of Selected Code Legislation (1955-1969): Analyses of key legislation by the Continuing Education of the Bar. In print at Stacks, KFC16 .R4 (1967/69 articles obtainable via scan/email service from NRLF, with specific citation).
University of the Pacific Law Review (and former titles) (1970-current): Each year's January issue features reviews of selected California legislation from the prior year. Via Hein Online (campus library terminals, or proxy access).
Indexes such as LegalTrac and Index to Legal Periodicals can help you find law review articles on your legislation and/or the subject of the legislation.
Also check the Main Library's A-Z Databases list for indexes and full-text databases to search newspapers and other journal articles. Select Database Type: News and/or type "california newspapers" in the search box at the top of the list to find sources. California Digital Newspaper Collection can be particularly useful.
It is sometimes effective to contact the bill's author; especially for recently enacted legislation (file materials or other leads may still be maintained for prior legislative years). Provide the year and bill number when requesting information. Check the Assembly's or Senate's website for phone numbers of current members. Former members may be less likely to have maintained materials, but you can try the Leadership Connect directory for current contact information.
Several state offices provide analysis and research on legislation. And don't forget about advocacy groups, research centers, think tanks and foundations that may have been interested in the legislation. Try the websites listed under Legislative & Policy Analysis Sources, especially for categories like "publications," "research," "news/press," etc.
For a fee you may have your search done by a commercial searching service, and since they have access to materials in Sacramento that we do not receive in our library, such a search may turn up useful information. Some services to try are: