THE COMMUTER AIR CARRIER DEPARTED MOAB, UTAH, AND FLEW TO GRAND JUNCTION, CO, VIA RNAV DIRECT MACKS INTERSECTION. AFTER CROSSING MACKS INTERSECTION, THE AIRPLANE TURNED RIGHT BUT INSTEAD OF INTERCEPTING THE LOCALIZER COURSE, THE AIRPLANE CONTINUED ON A SLIGHTLY DIVERGENT TRACK TO THE EAST OF THE LOCALIZER. THE PILOT TOLD CONTROL TOWER PERSONNEL, 'I'M SHOWING TWELVE MILES OUT ON THE ILS...GETTING REAL...ERRONEOUS SIGNAL, HERE. ANY COMPLAINTS?' THE PILOT WAS ADVISED NO DIFFICULTY REPORTS HAD BEEN RECEIVED. THE AIRPLANE IMPACTED A MESA ONE MINUTE LATER ABOUT FIVE MILES TO THE LEFT OF THE LOCALIZER COURSE. THE COCKPIT WAS DESTROYED AND NO MEANINGFUL INFORMATION WAS OBTAINED FROM THE NAVIGATIONAL RADIOS. ALL OF THE AIRPORT'S NAVIGATIONAL AIDS WERE LATER FLIGHT CHECKED AND NO DISCREPANCIES WERE FOUND. ALTHOUGH VMC PREVAILED AT THE AIRPORT, THE ACCIDENT SITE WAS ABOVE THE REPORTED CEILING HEIGHT.