On March 28, 1994, at 1630 hours Pacific standard time, a Mooney M-20C, N4045N, gear collapsed while landing on runway 14 at Hyampom Airport, Hyampom, California. The pilot was completing a visual flight rules personal flight. The airplane, registered to and operated by the pilot, sustained substantial damage. Neither the certificated private pilot nor any of the three passengers were injured. Visual meteorological conditions prevailed. The flight originated at Hayfork Airport, Hayfork, California, at 1615 hours. The pilot reported in a telephone interview conducted on March 28, 1994, that the landing gear is a mechanically operated system. During the landing roll, the landing gear handle disengaged from its latching mechanism and the landing gears retracted. He also said that he encountered turbulence when he extended that landing gear. The Safety Board retained Mr. Paul Israel, General Aviation Enterprises, Hayfork, California, to examine the airplane's landing gear system. Mr. Israel reported that he was unable to dislodge the handle (aka Johnson Bar) after placing the airplane on jacks with the landing gear extended. The handle was in the locked position. He also said that he did not find any landing gear system defects.