On May 28, 2005, about 1200 Pacific daylight time, a S.A. Centrair Pegase 101D, N70LE, made an off-airport landing and ground looped near Williams, California. The pilot was operating the glider under the provisions of 14 CFR Part 91. The commercial pilot, the sole occupant, was not injured; the glider sustained substantial damage. The local personal flight departed Williams Gliderport (CN12), Williams, about 1045. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot submitted a written statement. He reported that after being released from an aero tow at 3,500 feet mean sea level (msl), the glider encountered an immediate sink rate of 700 feet per minute (fpm). During the next 2 minutes, he found moderate and consistent lift in a mountain wave. After 20 minutes of good soaring conditions there was an abrupt transition to sinking conditions with a sink rate of about 700 fpm. He maneuvered on a southwesterly heading towards hills, anticipating lift in that area. However, the glider continued to lose altitude, as well as experiencing choppy low-level turbulence. The pilot noted his altitude was 2,800 feet. The pilot judged a return to the Gliderport to be uncertain and turned to a north-northwesterly heading in the direction of known airstrips. The pilot was able to regain some altitude to 4,260 feet. As he continued toward the airstrips, he reported that the glider could not maintain lift. He decided to make an off-airport landing. The glider landed on an unpaved fire road with upsloping terrain on the right-hand side. The road was on a north-south heading, and he made a landing to the south. The glider touched down aligned along the centerline of the road. The pilot reported that during the landing rollout, due to a combination of rising terrain on the right side and a crosswind, the right wing lifted up. The left wing contacted the surface, and the glider ground looped. The glider departed the road and came to rest after turning about 200 degrees to the left. The pilot stated that the glider had no mechanical failures or malfunctions. The pilot estimated that the surface winds at the time of the accident were 8 to 10 knots with gusts to 12 knots from a west-southwest direction.