During the second leg of a solo cross country flight, the student pilot reported that he became disoriented in mountainous terrain, and flew down a valley that he thought would lead him to his planned route. After entering the valley, the student pilot did not believe he had sufficient distance laterally to turn around, so he decided to initiate a climb to clear the ridge line in front of him. During the climb he heard the stall warning horn intermittently and realized he could not clear the ridge line ahead. The student pilot made an emergency landing into the rising terrain ahead of him and came to rest in the trees. During a postaccident interview, the student pilot reported that he didn't realize that he lacked the training and understanding for flight into mountainous terrain. The flight instructor who endorsed the student pilot's logbook for this route of flight reported that he should have provided "actual mountain flying training prior to a solo flight over mountainous terrain." The student pilot stated there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation. The left wing and fuselage were substantially damaged.