What happened
The pilot was flying at 3,500 feet AGL toward the western plateau when the aircraft encountered thermal activity consisting of approximately 2-4 knots of lift and 4-6 knots of sink. The pilot reported that the lifts were ill-defined and that the aircraft primarily encountered sinks.
As the altitude decreased to 2,500 feet AGL, the pilot turned back toward the departure airport. During this period, the glider continued to experience sink rates between 4 and 6 knots, prompting the pilot to search for a suitable field for an emergency landing. While overflying a potential landing field at 2,000 feet AGL, the pilot identified a fairly constant 6 knot sink rate. As the pilot approached the field, the sink rate increased, leading to a collision with trees at the approach end of the intended landing area.