I have not stayed at this site yet, but discovered it recently, and so I am adding it for people who are looking for group camping options in the Los Angeles area/ San Fernando Valley area. These sites can only be reserved by groups if you call the park office in advance.
It’s a short hike in from one trail that connects to Placerita Canyon Rd, or a ~1 mile hike from the Nature Center.
Picnic tables and water spigots are available in the group sites, with a port-o-potty nearby.
Beautiful stream/waterfall trail directly from the sites
More park camping info:
https://www.pcnca.org/park-rules.html
“ 17.04.390 Overnight camping restrictions -- Permit issuance conditions.
A. A person shall not camp or sleep overnight in any park except where a family-type camping area is so designated, and then only in accordance with the rules and regulations governing the use of such area. The director may issue a permit to any youth group of a character-building nature and to any special-interest group permitting its members as a group to camp overnight at a designated location in a park.”