On July 2, 2010, about 0800 mountain standard time, a Mooney M20F, N6802V, sustained substantial damage following a landing gear collapse during landing roll at the Cottonwood Airport (P52), Cottonwood, Arizona. The certificated private pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed for the cross-country flight, which was being operated in accordance with Title 14 Code of Federal Regulations Part 91, and a flight plan was not filed. The airplane had departed the Chandler Municipal Airport (CHD), Chandler, Arizona, about 0700, with P52 as its destination. In a telephone conversation and in a written report submitted to the National Transportation Safety Board investigator-in-charge (IIC), the pilot stated that when established on a four mile final and observing the green down and locked light, he reduced power and speed to 120 miles per hour (mph), executed the ‘GUMPS’ checklist and trimmed the airplane to 80 mph. All was normal and he felt a smooth touchdown, with an instantaneous drop of the plane onto its belly. The airplane then slid approximately 200 feet and came to rest on the runway. The pilot further stated in his report that one item he could not remember checking was the gear locked plate on the floor between the front seats. The pilot reported that later that day when the battery was hooked back up, it was seen that this plate was not slid completely into position. The pilot stated that if this had been noticed in flight he could have tried cycling the gear and seen to it that this plate was in the normal locked position. A Federal Aviation Administration (FAA) airworthiness inspector reported that an examination of the airplane revealed that it had sustained significant damage to the belly skin, but no damage to the main landing gear doors. The nose landing gear doors were damaged on the outer surfaces, which is the lower surface when the gear is up and the gear doors are closed. The inspector stated that the landing gear extension and retraction system is gear and push rod driven, and that a collapsing gear would have resulted in damage to those components; an inspection of the drive components found them undamaged. The inspector added that after jacking the aircraft up and cycling the landing gear several times, the electrical extension, alternate mechanical extension and landing gear position indicating systems worked properly. The inspector concluded that the landing gear was up and selected in the UP position when the airplane contacted the runway.