The glider pilot reported that he was towed from the airport to a ridgeline approximately 5 miles east of the airport. After being aloft for approximately one hour, the glider was blown to the downwind side of the ridge. The pilot reported, "...the wind blew the glider to the downwind side of the ridge." The pilot attempted to fly back to the area of lift, but was unsuccessful and elected to land in an open field on the ridge. During the landing rollout, the glider struck small trees resulting in substantial damage.