Forum member MudCamper from the calguns.net forum created a nice, concise document that describes the legality and options available for acquiring or building an AR-15 or AK-47 style rifle in California. Yes, for those of you reading this from free America (i.e. outside California) it may come to a surprise to know that it is still possible to legally own one of these rifles despite the California Assault Weapons Control Act, aka the California Assault Weapons Ban.
The pdf can be found here.