THE PILOT, ACCOMPANIED BY A PASSENGER, WAS LANDING A TUNDRA TIRE EQUIPPED AIRPLANE ON A REMOTE GRAVEL BAR ADJACENT TO A RIVER. DURING THE LANDING ROLL, THE AIRPLANE BEGAN TO TURN TO THE RIGHT. THE PILOT WAS UNABLE TO CONTROL THE AIRCRAFT AND IT GROUND LOOPED TO THE RIGHT. THE LEFT WING AND HORIZONTAL STABILIZER WERE DAMAGED WHEN THEY STRUCK THE GROUND. THE PILOT INDICATED THAT AFTER THE ACCIDENT, HE NOTICED A TAIL WIND OF ABOUT 4 TO 5 KNOTS FROM THE RIGHT REAR QUARTER OF THE AIRPLANE.