A C172 IN THE TFC PATTERN AT 1W1; HAD AN NMAC WITH A PA28 THAT WAS TRANSITIONING THE AIRSPACE.

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I WAS AT PATTERN ALT 1250 FT MSL APCHING (1W1); 3 SM FROM THE ARPT FLYING ABOUT 118 DEGS MAGNETIC HDG. I HAD CHKED 360 DEGS FOR TFC ABOUT 15 SECONDS EARLIER. SUDDENLY I SAW WHAT LOOKED LIKE A PIPER CHEROKEE ON THE EXACT HDG AS ME; PASS EXACTLY OVER ME BY ONLY ABOUT 175 FT SEPARATION AND FLYING ABOUT 30 MPH FASTER THAN ME. I WAS EXECUTING A 45 DEG ENTRY TO A L DOWNWIND FOR RWY 25 AT 1W1. I CONTINUED MY APCH AND LNDG AT 1W1. THE OTHER ACFT HAD CONTINUED ON ITS COURSE AND HDG. THE OTHER ACFT APPARENTLY NEVER SAW ME. HE APPEARED TO BE SET UP FOR A R BASE ENTRY FOR RWY 25 AT TTD. SO I CALLED THE TTD TWR AFTER LNDG AT 1W1; TALKED WITH CTLR; WHO SAID HE HAD A CHEROKEE CALL ABOUT THAT TIME TO TRANSIT THE CLASS D AND THEN TURN E TO FLY UP THE COLUMBIA RIVER GORGE. THE CTLR COULDN'T RECALL AN N-NUMBER FOR ME; HE SAID THE OTHER ACFT WAS FLYING 1500 FT MSL. ALTHOUGH I HAD MY XPONDER AND MODE C ON; HE SAID HE SAW ONLY 1 TARGET AT 1500 FT. DUE TO THE CLOSE PROX OF 1W1 TO TTD; I BELIEVE THE TTD TWR SHOULD ISSUE A GENERAL WARNING OF POSSIBLE 1W1 TFC; AND TO GIVE ALT SETTING AND ASSIGN 1500 FT IMMEDIATELY TO ANY ACFT CALLING THEM; THAT ARE IN CLOSE PROX TO 1W1.