On May 31, 2003, at 2000 Pacific daylight time, a Beech 35-B33, N5FL, sustained substantial damage during a gear up landing at Inyokern Airport (IYK), Inyokern, California. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot and three passengers were not injured. The cross-country flight originated from Reno/Tahoe International Airport (RNO), Reno, Nevada, at 1800. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot reported that upon entering the Inyokern area, he announced via radio crossing midfield to enter left traffic for runway 20. During the descent to traffic pattern altitude (TPA) it was bumpy. He slowed the airplane to lower the gear (he thought he did) and entered downwind. The flaps were extended while turning from base to final. The airplane touched down and skidded to a stop at the left side of the runway. The pilot was unsure if he inadvertently moved the gear handle up, or didn't put it down, but felt he was responsible for the error either way. The gear handle was found in the up position. No mechanical malfunctions were noted with the airplane.