Step 1. Locate the statute you're researching in the California Codes and note the numbers and years of the chapter laws that enacted/amended it.
California statutes are introduced as bills in either the Assembly or the Senate. Assembly bills are cited as A.B. # (the # indicates the order in which the bill was introduced in the legislative session) and Senate bills as S.B. #. After a bill is enacted, it is assigned a chapter number and published chronologically in Statutes and Amendments to the Codes. For example, the first statute enacted in the 1987-1988 legislative session would be published as Chapter 1 in Statutes and Amendments to the Codes.
If you're trying to determine when particular language was added to or amended in a California statute, you first need to figure out which legislative enactments added/amended the language. To do so, locate the California code section you are researching, then find and note the session law (chapter) numbers provided below the code section. For example, the code section in the image below was added in 1984 (during the 1983-84 legislative session) as part of chapter law 1514. It was amended in 1994 as part of chapter law 1294, which was introduced as Assembly Bill 314).
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 section that follows the text of the statute. 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, 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.