SMT BIZJET AND UNKNOWN ACFT HAD NMAC NEAR O69; CA.

Narrative

WE DEPARTED PETALUMA ARPT VFR AND CLBED STRAIGHT OUT TO 1200 FT MSL BEFORE COMMENCING A TURN L TO PROCEED DIRECT TO SAUSALITO VOR. ABOUT THE TIME WE INITIATED THE TURN; THE FO CONTACTED ZOA TO PICK UP OUR IFR FLT PLAN INTO OAKLAND. UPON MAKING CONTACT WITH ZOA WE WERE GIVEN A SQUAWK CODE. SIMULTANEOUSLY THE CTLR ADVISED A SMALL SINGLE ENG ACFT THAT WE WERE PASSING OFF HIS L SIDE ABOUT 1/2 MI. THE PLT OF THE SINGLE ENG ACFT REPLIED 'IF THAT'S THE JET THAT JUST LEFT PETALUMA; HE JUST WENT RIGHT OVER THE TOP OF ME; ABOUT 100 FT.' NEITHER MYSELF NOT THE FO SAW THE OTHER ACFT EITHER BEFORE OR AFTER HIS RPT. SINCE WE FLY INTO THE PETALUMA ARPT ABOUT 2-3 TIMES PER MONTH; WE ARE AWARE; AND EXTREMELY VIGILANT REGARDING THE NUMEROUS SMALLER AND SLOWER ACFT IN THE AREA; BUT WE DID NOT SEE THIS ONE! IF THE WX IS VFR WE ALWAYS DEPART PETALUMA VFR AND CONTACT ZOA AIRBORNE; SINCE IT IS ALMOST IMPOSSIBLE TO CONTACT THEM FROM THE GND AT PETALUMA. ONCE AIRBORNE; COM IS NORMAL. BECAUSE WE DID NOT SEE THE OTHER ACFT WE DO NOT KNOW EXACTLY WHERE HE WAS; NOR THE EXTENT OF VERT OR HORIZ SEPARATION.