ACCORDING TO WITNESSES, THE GYROCOPTER PLT TOOK OFF & TURNED ONTO A LEFT DOWNWIND TO STAY IN THE TRAFFIC PATTERN FOR RWY 17. ONE WITNESS STATED THAT THE GYROCOPTER TURNED ONTO FINAL APCH AT ABOUT 300 TO 400 FT AGL. TWO OTHER WITNESSES, WHO RESIDE APRX 1/4 MI NORTH OF THE ARPT, RELATED THAT THE GYROCOPTER FLEW LOW OVER THEIR PROPERTY AT ABOUT 150 FT WHILE TURNING ONTO FINAL. BOTH REPORTED THAT THE ENG WAS OPERATING & SOUNDED NORMAL. ONE INDIVIDUAL STATED THAT THE PLT WAVED AS HE PASSED OVER HIS BACKYARD. REPORTEDLY, THE GYROCOPTER FLEW LOW OVER POWER LINES, CLIMBED TO A MORE NORMAL ALTITUDE, THEN ENTERED A STEEP DESCENT & CRASHED. ONE WITNESS SAID IT STALLED. ANOTHER SAID IT FELL LIKE A ROCK. IMPACT OCCURRED ABOUT 200 FT SHORT OF THE RWY. NO PRE-IMPACT FAILURE OR MALFUNCTION WAS FOUND. LOCAL GYROCOPTER OPERATORS STATED THE PLT WAS TEACHING HIMSELF TO FLY DESPITE RECOMMENDATIONS TO OBTAIN INSTRUCTION.