Adventure Pass
A National Forest Adventure Pass is a paid permit required to park at some locations in the national forests of Southern California (Angeles, Cleveland, Los Padres, and San Bernardino).
Types of passes
Both daily ($5) and annual ($30) passes are available. When purchasing an annual pass, a second-vehicle pass is usually available for just $5 extra. A National Parks annual pass ($80) also is accepted. The pass, which comes with a hang tag to mount on the rear view mirror, can be ordered directly from the Forest Service or obtained more easily from various outdoor equipment vendors such as REI or Big 5. A list of vendors sortable by name or locality can be found here.
When a pass is necessary
Make sure to verify the following information before acting on it
Generally speaking, the Forest Service claims that an Adventure Pass is required for any extended use of the applicable national forests. This means that a pass is not necessary to drive through the forest, to stop for a few minutes at a scenic view, to use the bathroom, etc, but it is necessary whenever participating in recreational activities within the forest. See the official Forest Service page for more details on the Forest Service policy, and the list of locations that the Forest Service requires an Adventure Pass for may be found here.
The lawsuit Fragosa v Moore resulted in a ruling that requiring fees (Adventure Passes) when using undeveloped parts of the national forests violates the Recreational Enhancements Act, and therefore those fees are invalid. So, it is likely that a visitor may not be legally ticketed for parking for extended periods of time at an undeveloped area within the national forests. However, the Forest Service may still issue a ticket despite its illegality, and dealing with that ticket may require substantial effort even if it is eventually dismissed.
Consequences of not displaying a pass
Make sure to verify the following information before acting on it.
The first time (or first few times) a vehicle is ticketed for not displaying a pass, they will usually be given a "Notice of Noncompliance" which can be resolved by simply paying the cost of an Adventure Pass. After an unknown number of noncompliance notices (perhaps just one), a vehicle still not displaying a pass may be given a true citation that may carry a fine as high as $100.