On May 6, 2000, approximately 1500 Pacific daylight time, a Schweizer SGS 1-35 glider, N34173, collided with trees during a forced landing about three miles east of Seaside, Oregon. The commercial pilot, who was the sole occupant, was not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 pleasure flight, which departed McMinnville Airport, McMinnville, Oregon, about four hours earlier, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, he had flown to an area near Astoria, Oregon, and then attempted to soar south along the western side of the Coastal Range. He hoped to be able to fly south to Tillamook, and then cross back over the mountains and return to McMinnville. While proceeding south, he intended to land at Seaside, Manzanita, or Tillamook if he reached a point where it appeared he could not safely continue. Upon reaching an area about 10 miles southeast of Seaside, he elected to turn back to Seaside, as he felt that there was "no assurance" that he could safely continue on his planned route. Soon after turning toward Seaside, he entered an area of "strong sink" and the aircraft began to lose altitude rapidly. When he was about five miles from the airport, the pilot realized that he could not successfully reach Seaside unless he encountered an area of lift. Since there were no suitable landing-out areas in sight, the pilot continued toward the airport by following the Clark River Valley. When he reached a point approximately three miles east of Seaside, knowing that he could not continue much further, the pilot elected to make a controlled forced landing in some small deciduous trees adjacent to a road running through the valley he was following. Although the pilot was not injured, the aircraft sustained substantial damage when it collided with the trees.