Lots of organizations put on track days/ DE's in So Cal. Here is the schedule of major events for the PCA Zone 8.
http://zone8.pca.org/calendar.php
Local PCA chapters may have other events not listed here.
I run with Speedventures and the PCA. Both are good. While you do tend to see a lot more gray hair in the pits with the PCA there are some distinct advantages:
- Lower entry fees
- Very low cost/high quality performance driving schools
- Free tech inspection
- Free skilled instructors provided
- Free timing at most events
- It's a mostly Porsche event so you are not sharing the track with Nissan Sentra's and Dodge Vipers.
A $40 PCA membership will usually pay for itself on your first track day.
Whatever you choose, enjoy your time on the track. That is what these cars were designed for.