Locate the California code section you are researching, then find and note the session law (chapter) numbers provided below the code section. An example is "Added by Stats.1978 c. 458," which means the statute first appeared in the 1978 volume of Statutes and Amendments to the Codes as chapter law 458.
West’s Annotated California Codes ( KFC30.5W4 - 4th Floor Research Alcove) and Deering’s California Codes Annotated (KFC30.5 D4 - 4th Floor Research Alcove) provide the current version of the law and list all amendments to the code section in the History/Credits sections. The annotated codes may also provide references to interim hearings, committee reports, legislative counsel opinions, law revision commission reports, attorney general opinions, the California Code of Regulations, law review articles, and notes of court decisions. West's Annotated California Codes and Deering's California Codes Annotated are also available online on Westlaw and Lexis Advance, respectively (subscription required).
LegInfo.Legislature.Ca.Gov, the official website for California Legislative Information, provides free online access to the current California Codes. Below the text of each statute, there is a notation regarding the most recent legislative activity affecting that statute - the most recent amendment, for example.