On April 23, 2002, at 1012 Pacific daylight time, a Cessna 340A, N6304X, had the right main landing gear collapse during the landing rollout at General William J. Fox Field (WJF), Lancaster, California. The owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The flight originated from Four Corners Regional Airport (FMN), Farmington, New Mexico, at 0800. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written report by the pilot, he stated the approach and landing were normal. He touched down on the main wheels first, and then the nose wheel touched down. He rolled out approximately 1,200 feet, without applying brakes. Then, he heard a clicking noise coming from the right main gear and felt the right side collapse. He added full power to maintain right wing up and checked and confirmed three green lights on his landing gear indicator. The pilot slowly let the power subside and the airplane veered to the right side of the runway as the right landing gear collapsed. A Federal Aviation Administration (FAA) inspector reported that the landing gear collapsed during the landing rollout on runway 24, and determined that the airplane sustained substantial damage. He found the landing gear selector in the down position. Examination of the landing gear microswitches revealed they were dirty, but not cracked or broken. After maintenance personnel replaced the microswitches, the landing gear functioned properly.