2 SMAS HAD AN NMAC IN AN 'OTHER CTLED AIRSPACE.' ATC DID NOT SEE THE INTRUDER ACFT.

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I WAS ON A VFR FLT FROM VAN NUYS TO JOHN WAYNE ARPT ABOUT A MI OFF THE COAST LEVEL CRUISE; 3500 MSL; 090 DEG HDG; 130 KTS IN CONTACT WITH COAST APCH 124.65. APCH CALLED OUT TFC AT 12 AND 10 O'CLOCK. I SAW AN MLG HIGH AT 12 (NO FACTOR) AND A RED LIGHT SINGLE AT 10 (NO FACTOR). WITHIN SECONDS A THIRD PLANE SMA APPEARED AT 11 O'CLOCK; 3500 MSL; APPROX 220 DEG HDG. I JUDGED I WOULD PASS BEHIND AND STARTED TO BANK L; BUT BY THAT TIME I FELT HIS WAKE AND WAS ALREADY PAST HIM. COAST GUARD TOLD ME I COULD DSND TO 3000 MSL. OBSERVATIONS: I WAS AMAZED HOW FAST WE CLOSED AND HOW LITTLE TIME THERE WAS TO REACT. I WAS SURPRISED TO SEE A THIRD PLANE WHEN 2 WERE CALLED OUT AND I WAS WATCHING 2. I HAVE RELIVED THIS EVENT MANY TIMES OVER THE PAST 2 DAYS. THIS IS A HIGH DENSITY AREA; I'M A CFI AND I TEACH IN THIS AREA ALL THE TIME; BUT I HADN'T SEEN ANYTHING THIS CLOSE. I WAS AT THE RIGHT ALT; HAD THE RIGHT OF WAY; AND HAD RADAR TFC BUT COULD HAVE BEEN HISTORY! RECOMMENDATIONS: THE FLT SCHOOLS FROM THE S BASIN NEED A FEW MORE ISOLATED PRACTICE AREAS.