Laguna is a track to die for. I have seen some track day there in the past. I remember setting up in the padock while bike were doing track day. Buttonwillow right off I-5 was a good test track too for cars and seen many bikes there.
The tracks in California are from South to North:
Fontana - Nascar tri-oval with a road course in the infield - haven't ridden it so I can't say anything about it
Chuckwalla - out in the middle of the desert about 40 minutes east of Palm Springs - haven't ridden it but looks like fun as long as you are not going there in the summer (110 degrees +)
Willow Springs - Rosamond, CA about 90 minutes north and a little east of LA off HWY 14. The big track is fast, way fast and a blast to ride. Streets of Willow (the little track) is also fun but for different reasons. There are also other tracks like a flat track and some off road tracks there. I actually have not been down there for 10+ years but it is a great facility. I raced at WS for years.
ButtonWillow - right next to I5 straight west of Bakersfield - track surface is getting bad in a couple of spots but otherwise is a great first track because almost all of the sightlines are unobstructed. Basically zero elevation changes except for a couple of dirt piles they added. I have done several track days there and really enjoy it.
Laguna Seca, Monterey - awesome track. Surface is smooth and well maintained. Sightlines are ALL obstructed so that can be a real challenge for some. Awesome runoff. Corckscrew is breathtaking the first few times. I've done a few trackdays there and love that track as well.
Sear Point/Sonoma Raceway - about 10 minutes south of Sonoma - this track is a staple of tracks in the Bay Area. Surface is not great, runoff is not great sightlines are not great in many turns but still a lot of fun. I've done track days there a few times. Not my first choice as I prefer Laguna but there are a lot more trackdays at Sears than at Laguna and typically Laguna is $50-100 more than Sears.
Thunderhill, Willows, CA - about 2-2.5 hours north of Sears point just off I5. I have not made it up to a track day at Thunderhill yet but many of my friend have been there many times and it is on my todo list. Looks like a lot of fun and there are many trackdays there each year. Typically a little cheaper than Sears.