There is a difference with California legal and Federal legal emission requirements. However if the Subaru you're interested in buying is equipped with all the Federal required emission components (which is originally equipped with) it can pass the California smog check and register with the CA DMV.
The rule is any Federal Emission (49-state legal) USED vehicle which is equipped with the required Federal Emission Components is eligible for California registration as long as the vehicle's exhaust emissions fall within California's limits and the vehicle's emission system has not been tampered with.
