An instructor pilot and a passenger (a student pilot) departed North Richland Hills, TX at about 1700 hrs. The instructor flew to a recreational area and landed in an open nearby field. He gave airplane rides to various persons for about 1 1/2 hrs then parked the aircraft. By this time the aircraft was low on fuel. Reportedly, the student pilot elected to fly to an airport and purchase more fuel since other persons wanted rides. The instructor stated that the student took the aircraft without permission. The student flew to Meachum Field at Ft Worth, TX and purchased 10 gallons of fuel. He returned and flew over the recreation area at dusk. A short time later at about 2010 local time, the plane collided with rising terrain near the recreational area and the open field that was used for earlier landings. It was not determined whether the student was trying to land or just flying low. A toxicological check revealed the student's blood/alcohol level was 0.13%. The pilot's seat belt was not buckled.