On August 6, 2015, about 1030 Pacific daylight time, a tailwheel equipped Ryan Aeronautical ST3KR, N48701, was substantially damaged when it collided with an occupied riding lawn mower during landing at the Frazier Lake Airport (1C9), Hollister, California. The airplane was registered to, and operated by, the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The private pilot sustained minor injuries and the pilot rated passenger sustained serious injuries. The pilot rated occupant of the lawn mower sustained fatal injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight. The local flight originated from the Reid-Hillview Airport, San Jose, California, at 1000, with 1C9 as the intended destination.In a written statement to, and a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge, the pilot reported that he initially transmitted his intention of landing about 8 miles from the airport on the airport's common traffic advisory frequency (CTAF). The pilot said he then entered the airport traffic pattern on a right downwind for runway 23, reported that he was on right downwind and continued to announce his position on downwind, base, and final for the runway on the CTAF. The pilot stated that he landed slightly longer than normal, and during the landing roll, the airplane struck a lawn mower. The pilot further reported that he did not see the lawnmower while he was in the traffic pattern or during the landing sequence. Examination of the airplane by a Federal Aviation Administration (FAA) aviation safety inspector revealed that the fuselage of the airplane was structurally damaged. The lawnmower, yellow in color, remained partially underneath the engine of the airplane, with the front of the lawnmower facing in the direction of travel of the airplane. In addition, the inspector reported that the airplane also struck a parked vehicle, which was white in color that was parked adjacent to the lawnmower. A witness, who was located in the run up area for runway 23, reported that he saw the lawnmower on the right side of the runway. The witness said that during his taxi to the run up area, and during his run up, he never heard any radio communication from the person on the lawnmower, however, he did hear the pilot of the accident airplane report that they were 5 miles out, followed by a report on downwind. The witness further reported that he saw the accident airplane on final approach, just crossing the runway numbers about 50 to 70 feet above ground level, and that it seemed to be fast, as if he was conducting a long landing. He then observed the airplane land in a 3-point attitude, and shortly after, impact the lawn mower. The driver of the truck who was located adjacent to the lawnmower, reported that he was having a conversation with the person who was seated on a mower about an issue he was having with it not cutting properly. He stated that they were just past the turn off to the taxiway on the right side of runway 23, and at no time heard or saw the airplane prior to the collision. He further stated that the person on the lawnmower did have a headset connected to an aircraft transceiver; however, he did not have the headset on during their conversation. 1C9 is a non-towered airport, which features a single turf runway (5/23) that is 2,500 feet in length and 100-feet wide. In addition, the airport features a water runway located adjacent to the turf runway that is 3,000 feet in length and 60-feet wide. Review of the FAA Airport Facilities Directory revealed that at the time of the accident, no remarks were present for mowing operations. In addition, at the time of the accident, no Notices to Airmen (NOTAMS) were present for mowing operations. The Ryan Aeronautical ST3KR is a two-place, tandem configured, low wing, tailwheel equipped monoplane, manufactured in 1942. The airplane is commonly flown from the aft seat, which is located just aft of the wing. Visibility from the aft seat is limited in a three-point attitude due to the nose high angle and engine.