A CHRISTEN INDUSTRIES HUSKY A-1 OPERATED BY THE US BORDER PATROL AS A PUBLIC USE AIRCRAFT COLLIDED WITH FLAT DESERT TERRAIN. THE PILOT WAS VISUALLY TRACKING FOOTPRINTS NEAR THE US-MEXICAN BORDER. THE AIRCRAFT WAS OBSERVED ORBITING AT A LOW ALTITUDE SHORTLY BEFORE ENTERING A STEEP TURN DURING WHICH THE NOSE PITCHED DOWN. THE AIRCRAFT IMPACTED THE GROUND IN A NOSE DOWN ATTITUDE & A POST IMPACT FIRE ERUPTED. THE FLAPS WERE DETERMINED TO BE IN THE 20 DEG SETTING. THE REAR SEAT BACK ASSEMBLY WAS DETERMINED TO BE UNLATCHED AT THE TIME OF IMPACT, THE AIRPLANE FLIGHT MANUAL HAD PERFORMANCE INFORMATION CONCERNING STALL CHARACTERISTICS OF THE AIRPLANE. THE MANUAL INDICATED AN ALTITUDE LOSS OF 150 FT DURING POWER OFF STALLS. THE AIRCRAFT FLIGHT MANUAL INDICATED THE USE OF 30 DEG FLAPS FOR ALL FLIGHT MANEUVERS REQUIRING FLAPS.