At about 1400 Pacific time, a Cessna 172N nosed over during the landing roll after encountering snow at Hayfork Airport. The pilot was not injured. The flight had originated at Cottwood, Calif., earlier in the day and had most recently departed Hyampom, Calif., about 15 minutes earlier. The pilot said he was attempting a short-field landing to the snow-covered runway, but during the landing roll, snow accumulated in front of the nose wheel and caused the nose over. The pilot also said he saw tire tracks on the approach end of the runway prior to landing, but did not realize they were from a vehicle instead of an airplane until afterward.