AFTER BEING TOWED TO AN ALTITUDE OF 1,000 FEET MSL, THE PILOT INITIALLY CLIMBED AN ADDITIONAL 100 FEET. ABOUT 5 MINUTES LATER HE ENCOUNTERED AN AREA WHICH WAS NOT GENERATING ANY LIFT AND DECIDED TO TURN BACK TOWARD THE AIRPORT. WHILE FLYING AN UPWIND COURSE, WHICH WAS IN CLOSE PROXIMITY AND NEARLY PARALLEL TO THE NORTH SIDE OF A NEARBY RIDGE LINE, THE GLIDER ENCOUNTERED AN UNEXPECTED DOWNDRAFT. UNABLE TO MANEUVER OUT OF THE CONDITION, THE GLIDER WAS FORCED DOWN, IMPACTING STEEP, ROCKY TERRAIN. THE PILOT REPORTED THAT THE PREVAILING WINDS AT THE ACCIDENT SITE WERE GUSTING FROM THE SOUTHEAST.