THE ACFT CRASHED AT A REMOTE LANDING SITE WHILE ON A SEISMIC OPERATION. THE PLT STATED THAT HE DEPARTED A RIDGE- TOP WITH INTENTIONS OF DROPPING OFF 2 TO 4 PASSG AT ANOTHER RIDGETOP LOCATED ONE-HALF MI SOUTH. THE INTENDED LDG POINT WAS A NARROW RIDGETOP AT 6000 FT MSL, SURROUNDED BY RUGGED TERRAIN & NUMEROUS HIGH PEAKS TO 8000 MSL. HE STATED THAT THE APPROACH WAS MADE TO THE SOUTHWEST WITH THE WIND AT THE 11 O'CLOCK POSITION. HE FURTHER STATED THAT 'AT APPROX 20 FT ABV TOUCHDOWN I ENCOUNTERED A DOWNDRAFT/WIND SHIFT WHICH INDUCED A HIGH VERTICAL RATE OF DESCENT. I DID NOT HAVE SUFFICIENT ALTITUDE TO ABORT THE APPROACH. THE ACFT LANDED HARD ON THE NOSEWHEEL, STABILIZED AT A HOVER FOR ABOUT TWO SECONDS, THEN ROLLED ONTO ITS RIGHT SIDE. I SUSPECT THAT THE DAMAGED NOSE GEAR STRUT INTERFERED WITH THE FLT CONTROLS AFTER INITIAL IMPACT.' THE PLT STATED THE ACFT OPERATED IN A NORMAL MECHANICAL MANNER PRIOR TO THE ACTUAL ACCIDENT SEQUENCE.