On May 29, 2000, approximately 1145 Pacific daylight time, a Russia AS+ sailplane model AS-4, N1995M, registered to Evergreen Soaring, Inc., and being flown by a private pilot, sustained substantial damage during an off-airport landing approximately four nautical miles northwest of Ephrata, Washington. The pilot was uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was personal, was operated under 14CFR91, and originated from Ephrata, approximately 15 minutes prior to the accident. The pilot reported that after departing Ephrata and flying west several miles, he released from the towplane about 4,300 feet above mean sea level (MSL). Ephrata airport elevation was 1,272 feet MSL. Once released from the towplane he resumed level flight, and thermalled for several minutes beneath a cumulous cloud while flying over the ridgeline west of Ephrata. After regaining altitude back to 4,300 feet MSL, the pilot noted that lift began to dissipate and he turned west in search of improved lift conditions. Approximately one minute later he encountered heavy sink and continued flying west for another minute during which the sink conditions continued. He then turned north but the sink conditions persisted. The glider's altitude was approximately 3,200 feet MSL, and he decided that he could not make a safe return to the Ephrata airport from his current location. The pilot once again turned west towards a cumulous cloud "thinking that I would find lift there" but did not. He then noticed a large plowed field and turned north on a direct line towards it. He reported that he "was still in considerable sink and ended up landing approximately 1/4 to 1/3 mile south of the plowed field in a sagebrush field." He reported that upon ground impact the glider immediately ground looped to the right damaging the tail-boom. In the data element titled "Recommendation (How could this accident have been prevented)" on the pilot's completed NTSB Form 6120.1/2, the pilot wrote: "Pilot should have immediately turned back to [the] departure airport when heavy sink was encountered."