On August 22, 2004, about 1000 Pacific daylight time, a Piper PA-30, N8475Y, experienced a landing gear collapse while on the landing roll at the Auburn Municipal Airport, Auburn, California. The pilot was operating the airplane under the provisions of 14 CFR Part 91. The commercial pilot and one passenger were not injured; the airplane sustained substantial damage. The personal cross-country flight originated from Ralph Wenz Field Airport, Pinedale, Wyoming, about 0700, with a planned destination of Auburn. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written statement, the pilot reported that while entering the proximity of the airport, he extended the landing gear, noting that the landing gear indicator lights did not illuminate green. As the airplane continued on the downwind leg for runway 07, the landing gear indicator lights finally illuminated, indicating that the landing gear were in the extended position. After a normal touchdown, the airplane rolled down about 1/3 the runway length and the landing gear collapsed. During the collapse, the airplane rotated about 120 degrees before coming to rest. An Auburn Police Department sergeant was on the airport making a routine check of the field. He stated that he heard the sound of grinding metal and saw the airplane crash onto the runway. In his report, the sergeant said that he talked to the pilot immediately after the accident. The pilot informed him that prior to touchdown, he had mistakenly moved the control lever for the wing flaps, rather than the control lever for the landing gear, which resulted in the airplane making a gear-up landing. In a telephone interview, an airplane mechanic reported that he conducted an inspection of the airplane after the accident occurred. He stated that from looking at the propeller slash marks on the runway, it was apparent that the left main landing gear collapsed first, followed by the right main landing gear several seconds later; the nose gear appeared to collapse when the airplane came to rest. The airplane was hoisted by a truck and the mechanic manually extended the landing gear to a down and locked position. After looking inside the cockpit, he observed that the landing gear control lever was in the down, extended position, and the wing flap control lever was in the up, retracted position. During his inspection, he found no defects or faults that could have resulted in a landing gear failure. He further noted that the squat switch was intact and operated normally. This accident was upgraded from an incident on September 21, 2004, based on a damage assessment by the Federal Aviation Administration (FAA). The airplane incurred damage to the left wing, fuselage, and landing gear doors. The FAA inspector who examined the airplane after the accident, stated that the main landing gear doors were crushed outward; an indication that the landing gear were extended when the collapse occurred.