THE PILOT SAID THAT PRIOR TO DEPARTURE AT EL PASO SHE VISUALLY LOOKED IN EACH FUEL TANK AND ESTIMATED THEY WERE TWO THIRDS FULL. SHE DID NOT PHYSICALLY MEASURE THE FUEL QUANTITY. THE LEFT FUEL GAGE WAS KNOWN TO BE INOPERATIVE BY THE PILOT. ON A TWO MILE FINAL APPROACH TO TUCSON THE ENGINE BEGAN TO SPUTTER. THE PILOT SWITCHED FUEL TANKS AND THE ENGINE QUIT. THE AIRCRAFT COLLIDED WITH ROUGH TERRAIN DURING THE SUBSEQUENT FORCED LANDING ATTEMPT IN A DESERT AREA EAST OF THE TUCSON AIRPORT. THE AIRCRAFT WAS EXAMINED BY FAA INSPECTORS. THE LEFT FUEL TANK WAS COMPLETELY DRY AND THE RIGHT TANK CONTAINED ONLY RESIDUAL FUEL. FUEL SYSTEM CONTINUITY WAS ESTABLISHED. THE FAA INSPECTORS REPORTED THAT THE OPERATOR KNEW ABOUT THE INOPERATIVE FUEL GAGE PRIOR TO THIS FLIGHT BUT DID NOT REPAIR IT DURING THE LAST MAINTENANCE PERIOD. AN OPERATIVE FUEL QUANTITY INDICATING SYSTEM IS REQUIRED BY REGULATION FOR FLIGHT.