According to the pilot, this was intended as an “out & return” recreational flight. He intended to climb via thermals to get across a five-mile gap between ridges, but was unable to gain altitude. He then attempted to turn to a “spur” that was separate from the main ridge to gain lift, but while performing the maneuvers, the glider continued to lose altitude “in sinking air.” The glider subsequently impacted trees and came to rest inverted, seriously injuring the pilot. The pilot reported that there were no mechanical problems with the glider. He stated that in retrospect, he should have released the 10 gallons of water ballast in each wing and deployed positive flaps. A weather observation taken approximately at the time of the accident, 35 miles from the accident site, recorded the wind as 290 degrees at 13 knots, gusting 20 knots.