CESSNA 206 ON LNDG ROLL SIGHTS A BONANZA TAXIING ONTO THE RWY. A UNICOM OPERATOR OBSERVER YELLS STOP AND BONANZA PLT DOES SO A RPTR PREPARES TO TAXI ONTO THE GRASS TO AVOID A COLLISION.

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I WAS LNDG ON RWY 16 AT (5T5) WITH THREE CAP CADETS ON BOARD. I HAD TOUCHED DOWN; AFTER MAKING 3 CALLS ON APCH; ONLY TO HAVE A BONANZA ALMOST TAXI ON TO THE ACTIVE RWY TO BACK TAXI FOR TKOF. HE STOPPED WITH HIS PROPELLER APPROX 3 FT FROM THE RWY W EDGE. I HAD MOVED TO E SIDE OF RWY PREPARED TO TAKE THE GRASS. HE INDICATED HE WAS 'MESSING WITH HIS GPS' AND NOT WATCHING. THE TRULY SAD SIT IS THERE IS A PARALLEL TXWY TO TAKE HIM TO 16 WITHOUT HAVING TO BACK TAXI ON THE RWY AND CREATE THIS POTENTIAL HAZARD. I WAS TOO SLOW TO EFFECT A GAR AT TIME HE STARTED ROLLING FORWARD; BUT FEEL I WOULD HAVE BEEN ABLE TO GET OFF THE GRASS TO AVOID COLLISION. SEVERAL WITNESSES INCLUDING THE ARPT MANAGER WITNESSED THIS EVENT. I RETURNED TO THIS ARPT ABOUT AN HOUR LATER AS ANOTHER CAP ACFT HAD UNRELATED MAINT PROBS AND THE WITNESSES; WHO WERE SUPPORTING A CROP DUSTER WERE AGHAST AT WHY OTHER PLT HAD NOT USED TXWY AND HAD ALLOWED HIMSELF TO MOVE TOWARD RWY. I ASKED PLT ON RADIO WHAT HE WAS THINKING ABOUT AND HE ADVISED HE WAS PAYING TO MUCH ATTENTION TO GPS AND DIDN'T REALIZE HE WAS MOVING . HE NEVER DID EXPLAIN WHY HE DID NOT USE TXWY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE WAS CONCENTRATING ON THE FLAIR AND DID NOT SEE THE OTHER ACFT UNTIL ON THE ROLL AND TOO SLOW TO GAR. THERE HAD BEEN NO COMMUNICATION FROM THE OTHER ACFT. THE GRASS WAS WET AND SOGGY; BUT A BETTER OPTION THAN HITTING THE BONANZA SO HE WOULD HAVE TAKEN THAT OPTION HAD THE ACFT NOT STOPPED. HE FLIES OVER THIS ARPT FREQUENTLY AND IS AWARE OF THE CONFIGURATION. RPTR ATTENDED A NON-TWR SAFETY SEMINAR RECENTLY AND FELT IT WAS VERY GOOD INFO.