According to the student's statement, the aircraft was about 5 miles out from the airport descending toward the traffic pattern when the engine suddenly began to run rough and quit intermittently. The pilot was unable to affect an engine restart and the aircraft collided with orange trees about one half mile short of the runway. The student pilot was on a solo cross country round robin flight from Van Nuys, California, with planned stops at Paso Robles and Porterville for a total distance of about 400 statute miles. The distance flown from Van Nuys to Porterville with the stop at Paso Robles was about 270 miles. The investigation revealed that the student departed Paso Robles at about 1645 hours for Porterville and did not refuel the aircraft at Paso Robles. The aircraft was examined by FAA airworthiness inspectors who found no fuel in the fuel lines or carburetor bowl. No fuel spillage or odor was detected in the soil beneath the aircraft. The fuel tanks were ruptured in the impact sequence with the orange trees.