California State University Fullerton Arboretum (Fullerton, CA)
I learned about this location via a doll meet up on Den of Angels. While Fullerton may appear like you typical urbanized Orange County town, the arboretum on the Fullerton campus takes you away to a different time and place.
There is a lake and a nice grassy area that is picnic friendly. There are also various gardens and an old Victorian house in the arboretum. When we did the doll gathering, we kept it small (less than 30 people) and we kept photo taking where it does not bother or disturb guests. This is a nice place for a small cosplay gathering that calls for a nice outdoor shots.
Downtown Fullerton is just a hop, skip, and a jump away from campus. There are plenty of restaurants such as the Old Spaghetti Factory and Tranquil Tea Lounge. A variety of restaurants are available for cosplayers and photographers on a budget.
Transit and Parking
OCTA buses run through CSU Fullerton. Check schedules accordingly. The Fullerton train station is close enough to campus where one can catch an OCTA bus. Parking is free on weekends.
For more information on the Fullerton Arboretum, you can visit their website.