I found some additional info from their website.
http://www.chp.ca.gov/html/militarydrivers.html
"Registration and Smog Laws
A car registered in another state that has no smog devices is legal to drive in California as long as it is equipped as required in the other state.
Vehicles are prohibited from emitting excessive exhaust and will be cited for air pollution, even if the car is registered in another state.
All new unregistered motor vehicles that are brought into California whose odometers read less than 7,500 miles must meet smog requirements and must be equipped with a California emission system before they can be registered.*
New Vehicles - a new vehicle that was previously registered in your state of residence or last state of active military duty does not have to be equipped with a California emission system.
Used Vehicles - Most used vehicles previously registered in another state must meet Californias emission standards before registration will be issued."