B737 FLC INITIATE EVASIVE MANEUVERS AWAY FROM UNIDENTED TCASII ACFT AT SAME ALT; DISREGARDING SCT CLRNC TO MAINTAIN ASSIGNED ALT.

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WE WERE ENRTE TO BURBANK FROM BULLHEAD CITY. THE SOCAL FREQ WAS 134.2. THE TCASII HAD A STRANGE LOOKING TARGET APCHING OUR POS; OUTSIDE THE RING YET; BUT COMING STRAIGHT FOR US. WE WERE JUST N OF THE RIDGE. (2 ACFT WERE ON TCASII; BUT APPEARED TO BE 1.) SOCAL CALLED OUR TFC AT 5000 FT. OUR CLRNC WAS TO 6000 FT AND A HDG OF 160 DEGS. WE WERE THERE. THE TCASII DID NOT LIKE THIS; AS THE TARGET CROSSED THE RING INTO OUR SPACE. THE TCASII SAID OUR TARGET WAS AT OUR ALT; THOUGH SOCAL CALLED IT 1000 FT BELOW US. IT WAS CLR AND I GOT A VISUAL ON THE CESSNA AT 5000 FT. WE COULD NOT SEE THE ONE THAT WAS AT OUR ALT AND COMING STRAIGHT AT US. I BEGAN TO DSND AND TURN AWAY; FIRST L THEN R; TRYING TO GET AWAY FROM THE TARGET AT OUR ALT; PROMPTED BY TCASII ALSO. I DON'T BELIEVE SOCAL SAW THE VFR TFC AT OUR ALT; THOUGH HE DID CALL THE IFR TFC BELOW US. I DON'T BELIEVE WE BROKE ANY RULES; BUT THE SIT SCARED ME AND GOING INTO BURBANK AND ONTARIO WE USUALLY GET A TCASII SOLUTION AT LEAST ONCE EVERY TRIP; UNLESS IT IS IFR CONDITIONS. THE TARGET SOCAL CALLED WAS THERE AND AN ADDITIONAL TARGET WAS DIRECTLY ABOVE HIM; WHICH I BELIEVE ATC COULD NOT SEE. HE VECTORED US TOWARD THAT TARGET AND TOLD US NOT TO LEAVE 6000 FT. THE TCASII SAVED THIS DAY.