These are the two systems I've seen on CA cars. A sticker under your hood will let you know if your car has any of these systems.
ULEV2 Emissions Equipment
REQUIRED in California, Massachusetts, Maine, New York and Vermont.
Anyway, ULEV II (Ultra Low Emissions Vechicle, Tier II) is pretty clean. It's the second-cleanest tailpipe emissions rating there is. SULEV II (Super Ultra Low Emissions Vehicle, Tier II) is the cleanest. (although technically ZEV (Zero Emissions Vehicle) is cleaner still, with no tailpipe emissions)
PZEV (Partial Zero Emissions Vehicle) vehicles are all SULEV II. In addition, PZEV engines are specially designed so that they have no evaporative emissions, which aren't directly covered by the tailpipe emissions ratings. They also come with 10-year, 100,000-mile warranties on their emissions equipment.