CONFLICT BTWN A C414 TWIN AND A PIPER PA28 ON A DOWNWIND LEG TO AN UNCTLED ARPT WHEN THE RPTR PASSED BY THE PIPER.

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THE ARPT SITS IN AN E/W VALLEY WITH RISING TERRAIN 1/2 NM N OF THE RWY AND LESS THAN 2 NM S. TFC PATTERN IS FLOWN WIDE ON THE S SIDE OF THE FIELD TO MINIMIZE NOISE OVER POPULATION AND BECAUSE OF TERRAIN AND HIGH FIELD ELEVATION (MORE THAN 6700 FT). BOTH ACFT WERE IN CONTINUOUS RADIO CONTACT WITH ALL POS RPTED. I ENTERED EXTENDED DOWNWIND L TFC RWY 26 (L35) SLOWING TO APPROX 100 KTS. THE PIPER (ACFT #2) WAS ALREADY MID-FIELD TRAVELING MUCH SLOWER (ESTIMATED 80 KTS). APPROX 1/2 MI BEYOND THE NUMBERS OF RWY 26; MY ACFT (#1) CAUGHT UP WITH ACFT #2 AND PASSED 100-200 YARDS OFF HIS R WING. ACFT #2 CONTINUED DOWNWIND AND SET UP FOR A LONG FINAL (A STUDENT WAS PRACTICING). ACFT #1 CONTINUED DOWNWIND UNTIL TERRAIN ROSE ON THE E; TURNED BASE AND FINAL; OVERFLEW THE ARPT AND RE-ENTERED FROM XWIND. THE SIT WAS HANDLED SMOOTHLY BY BOTH PLTS BUT THE SPACING WAS CLOSER THAN OPTIMAL. ON FURTHER THOUGHT I BELIEVE MY BEST COURSE WOULD HAVE BEEN TO CLB WELL ABOVE THE PATTERN AND OVERFLY; RE-ENTERING FROM XWIND; HAVING PASSED WELL ABOVE ACFT #2.