Been a while since I lived in Cali...
California gun laws are fairly restrictive compared to the rest of the country:
1. all handguns must be transferred through a dealer, including private sales, inheritance, and intra-familial transfers.
2. all handguns other than privately transferred versions are subject to the "safe handgun roster" mandating specific features (some of which are impossible or utterly unrealistic).
3. there is a CA specific background check (the DROS process) that works with the western states (CA, NV, OR, WA, AZ) that is performed in addition to the federal background check. the DROS process is an additional fee, and is more limited in scope but more restrictive as to what can make someone a prohibited person. for example the DROS can give a "deny" if someone has unpaid child support, or if you have any sort of financial obligation for wage garnishment.
4. violence restraining orders are available in CA law so that someone who feels that someone else they are acquainted with is a danger to themselves or others can have that person's firearms confiscated.
5. CA has a handgun safety test that mandates specific knowledge and compliance with CA firearms laws.
6. specific cities have outright banned gun stores and many Bay Area cities/counties are actively closing gun ranges.
7. CA has additional fees for every step of the gun ownership process, making firearms expensive within the state.
8. CA has a limited market due to very restrictive import laws that drive up the price of firearms.
9. CA has more recently banned the sale of ammunition except through face to face transactions through a licensed ammunition dealer (for an additional fee) and restricted the amount of ammunition and type that can be bought.
10. most CA counties forbid anyone not wealthy or politically connected from obtaining concealed carry permits in practice. it took decades of lawsuits to force a couple counties on the issue.
11. CA has a 10 day waiting period for firearms transactions.
12. CA has a proof of residency requirement for all transfers, and for handguns you also need an additional proof of identity. there are several restriction on the allowed types.
13. CA has a 10 round magazine limit. many weapons may not have magazines of a legal size in existence. possession of magazines can be a misdemeanor or felony, depending.
14. violating most CA firearm laws is a felony and will permanently revoke your ability to own / possess firearms in the state.
15. there are also numerous transportation laws and storage laws regarding firearms (mandatory locks for handguns, for a fee, et c)
16. each dealer has many hoops to move through to legally transfer a firearm between dealers, over state lines, and into a resident's hands. most guns that are available out of CA may not qualify for individual transfer inside CA. the time and cost (licensing, paperwork, affidavits, mandatory forms acknowledging various things) generally have made the process onerous enough that many opt to just not bother with legal channels or opt to not own a firearm.
there are other laws that apply to long arms (rifles, shotguns), and NFA items (suppressors, machineguns, short barreled shotguns, short barreled rifles, destructive devices, and any other weapon). i'm also not going to include CPSC prohibitions against murder or bodily harm, or touch on any federal laws. the above is more or less CA laws as they commonly pertain to handguns.
the reality is that someone intent on committing a violent crime will obtain and use a gun towards that purpose more often than not, and no laws on the books will change that without either a magic crystal ball or some truly Orwellian levels of enforcement.
