You may start out with a citation to the California codes or with a bill number (and year) that created or amended the law. Either way, begin your research with the annotated codes to find commentary, analysis, or clues to help locate the relevant phase(s) of legislative history.
For example, if you determine that a 1997 bill changed a critical part of the law, and you are interested in the legislative intent that behind that change, a Law Revision Commission Report dated 1997, or an article published in 1998 might give leads to key pieces of the legislative history or insights into the legislative intent of that specific language and the reasons for changing it.
Online—for any of the services below, in the search box on the main page, type your California code section (e.g., CA Family Code § 2312) and click search.
The annotations available in West's and Deerings versions of the California codes are not the same, so check both. If you have access, also check Lexis+ or NexisUni (both cover Deering's) and Westlaw (covers West's), as there may be added material online.