You should never pull over alongside a highway or near on ramps and off ramps.
Cal Trans says this can be especially dangerous for big rigs who are trying to get by.
It can also create traffic congestion.
The California Highway patrol is helping with the effort - and says vehicles found parked illegally on the side of the road - will be cited or towed for public safety.
You can find a map of California State Parks - just go to parks.ca.gov.