I’ve been a resident for more than 3 years so all that was needed was an affidavit showing that I was a resident for more than 3 years. So I myself am not sure what documents you would need.
When my kid attended CA public schools from K-12, every year 2 forms of ID was asked - 1) a document showing that you lived in the school district, ie a mortgage statement or lease agreement and 2) a utility bill, which we provided an electric bill. For UC tuition purposes, since current residency and intent of future residency is required, in addition to the above, you possibly may need to show tax statements and driver’s license, and maybe other forms showing a California address as well.