Read the uncodified law - the "chapter" or "session" law - to trace back the language of the law and determine how each amendment affected the law.
For chapter laws passed since 1999, you can find the full text of the chapter law under the Bill Information tab on LegInfo. Just enter the statute year and chapter number in the search box.
California session laws are published in Statutes and Amendments to the Codes ( KFC25 - 4th Floor Research Alcove). The library has the print version of Statutes and Amendments to the Codes for the years 1849 through 2008.
Statutes and Amendments to Codes is also available online on the website of the Office of the Chief Clerk of the Assembly. Click on the link for the specific year, then click on the link to the volume that contains the chapter law you're researching. A PDF containing the chapter laws in numerical order will open.
After you determine which chapter law introduced or amended the statutory language you're researching, you need to identify the bill number for that chapter law. For chapter laws enacted since 1994, you can find the bill number in the Credits/History that follow the text of the code section on Westlaw and Lexis Advance..
For older enactments, you will need to use the chapter number to find the bill number. The Summary Digest ( KFC5 - 5th Floor Stacks) is a good place to locate the bill number, a summary of the bill’s text, and its effective date. Beginning in 1967, the Summary Digest is published in the last volume of Statutes and Amendments to the Codes, which is available online on the website of the Office of the Chief Clerk of the Assembly.
Prior to 1967, the first volume of every year's Statutes and Amendments to the Codes includes a chart called the Table of Laws Enacted, which has a conversion chart for chapter number to bill number.
The Summary Digest [ KFC 5 - 5th Floor Stacks] is available at UC Hastings for 1949-51 & 1960-2008.