AT ABOUT 0530 PST, THE PILOT DEPARTED FROM HIS HOME AT RIDGE FIELD, WA ON A FLIGHT TO HILLSBORO, OR. ACCORDING TO THE PILOT'S INSTRUCTOR, THE NORMAL ROUTE USED FOR THIS TRIP WOULD BEEN TO PROCEED ON A SOUTHERLY HEADING TO CORNELIUS PASS, GO THROUGH THE PASS, THEN CONTINUE TO HILLSBORO. THE HELICOPTERCRASHED ABOUT 2.5 MI NORTHWEST OF CORNELIUS PASS. THE 0548 PST HILLSBORO WX WAS 1400 PTLY OBSCD, 3600 OVC, VIS 7 MI, TEMP 45, DEW PT 43, WIND 170 DEG AT 10 GS'TG 30 KTS. THE ELEVATION AT HILLSBORO WAS 204 FT, THE CRASH SITE WAS AT ABOUT 900 FT. THE PILOT'S INSTRUCTOR WAS SEARCHING THE AREA AT 0200. HE STATED THE CRASH SITE WAS OBSCURED BY CLOUDS, THERE WAS STRONG TURBULENCE, THE WIND WAS GUSTING FROM THE SOUTH AT 30 TO 40 KTS, AND THERE WAS HEAVY RAIN. AN EXAMINATION OF THE SITE REVEALED THE HELICOPTER HAD COLLIDED WITH TREES ON A STEEP SLOPE WHILE IN A TURN. NO PREIMPACT/ MECHANICAL MALFUNCTION OR FAILURES WERE FOUND THAT WOULD HAVE ATTRIBUTED TO THE ACCIDENT.