The law that establishes advance directives in California is the Health Care Decisions Act. It is based on the Uniform Law Comission's Uniform Health Care Decisions Act. It is in the California Probate Code, at Sections 4670 through 4806.
Below is a selection of sample advance directive forms. Note that you are NOT required to use the statutory form (Probate Code Section 4700). If you wish to, it is at Probate Code Section 4701. All of the forms below are pdfs.
Information about advance directives may be registered with the California Secretary of State. Note that this is NOT required to have a valid advance directive (Probate Code 4803). It is voluntary, and there is a $10 fee.