Every forest has its own district rules. In addition to being posted with signage, the ranger district states the following. I also saw large groups of cars ticketed for parking outside of locked gates and alongside highways.

https://www.fs.usda.gov/recarea/psic...80379&actid=34

Please observe these requirements when dispersed camping:
Plan your trip; phone ahead for restrictions and special regulations.
Dispersed camping and parking is allowed in designated sites only.. Do not create resource damage by driving off-road, beyond designated parking locations, or behind barriers. Parking should be within 30' of site markers.