After searching the forum and not finding any GBers in Orange County, CA, I am starting a new thread for anyone in my area that would like to meet up or knows of open gyms.
Yorba Linda Gymnastics holds open gym nights every other Friday 7-9pm for $10 a visit. You can use the equipment to train strength, tumbling, or skills. Most of the attendees are young students or young men practicing parkour skills.
A friend of mine said New Hope Academy of Gymnastics holds open gym Tuesday nights at 7-9pm. He mentioned the facility itself is huge and has a lot to offer as far as equipment. I would call first to get info: (714) 556-8050
Other than these places, the OC seems pretty limited. I am working with a friend of mine who owns a Crossfit gym to offer a time for open gym. If anyone here is interested, please let me know so I can let him know. His gym is in Fullerton.