NMAC BTWN A CESSNA CITATION 11 C550 CLBING ON A SID DEP 3 MI FROM ARPT OF DEP AND A PIPER CHEROKEE PA28 COMING ACROSS THE C550 FLT PATH AT NEAR TO THE SAME ALT. THE CITATION CAPT TOOK EVASIVE ACTION BY DSNDING AND TURNING.

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OUR ACFT WAS CLBING TO OUR INITIAL ASSIGNED ALT IN OUR IFR CLRNC OF 4000 FT MSL. WE WERE FOLLOWING THE BUCHANAN 7 SID WITH THE REJOY TRANSITION. VISIBILITY WAS GOOD AND THE WX WAS NOT A FACTOR. SHORTLY AFTER DEP; CONCORD TWR HANDED US OFF TO TRAVIS DEP. AS I SWITCHED FREQS; I HEARD TRAVIS COMMUNICATING WITH ANOTHER ACFT. I WAITED TILL THEY FINISHED AND MADE MY INITIAL CALL. THERE WAS NO ACKNOWLEDGEMENT AND NO COM FROM TRAVIS. AT THIS TIME THE CAPT BEGAN THE TURN OUTBOUND ON THE 071 DEG RADIAL OF CCR CLBING THROUGH 1800 FT. I CONTACTED TRAVIS AGAIN AFTER NOTICING TRAVIS WAS COMPLETELY SILENT. AGAIN THERE WAS NO REPLY. IMMEDIATELY AFTER; I SAW A PIPER AT ABOUT 2 O'CLOCK POS FLYING PERPENDICULAR TO OUR COURSE AND HIGHER. AFTER A COUPLE OF SECONDS; I REALIZED IF THINGS CONTINUED WE WERE GOING TO HIT THIS ACFT. I IMMEDIATELY NOTIFIED THE CAPT AFTER REALIZING THIS. THE CAPT TOOK EVASIVE ACTION; WHICH INCLUDED A DIVING L TURN. AS HE DID THIS; THE PIPER BEGAN A SLOW TURN TOWARD US COMING VERY CLOSE TO A COLLISION. ALMOST IMMEDIATELY; TRAVIS ASKED US IF WE WERE ON THE FREQ; WHICH I REPLIED AFFIRMATIVELY; AND TOLD HIM OF THE NEAR MISS. HE MADE NO COMMENT. IN HINDSIGHT; I REALIZED MY VISION OF THE ACFT WAS BLOCKED BY THE WINDOW POST UNTIL THE ACFT WAS VERY CLOSE. BY THIS TIME THE CLOSURE RATES OF THE ACFT WERE SIGNIFICANT. IT IS IMPORTANT TO REALIZE THE VISUAL LIMITATIONS OF YOUR ACFT; INCLUDING THE CITATION II; WHICH HAS EXCELLENT VISIBILITY. CONTRIBUTING WAS TRAVIS'S DELAY IN ESTABLISHING RADAR CONTACT. IT DID NOT APPEAR THAT TRAVIS WAS BUSY BASED ON THE VOLUME OF RADIO TFC BEFORE AND AFTER THE INCIDENT.