On March 18, 1999, at 2138 mountain standard time, a Cessna 172G, N1321F, owned and operated by the pilot, was substantially damaged during a forced landing following a partial loss of engine power while in cruise flight near Agate, Colorado. The private pilot and one passenger received minor injuries. The aircraft was being operated as a personal cross-county flight under Title 14 CFR Part 91, and no flight plan was filed. The flight originated from Kit Carson County Airport, Burlington, Colorado, at 2100, and was en route to Centennial Airport, Englewood, Colorado. Visual meteorological conditions prevailed. According to the pilot, she had stopped in Burlington to "top off" the fuel tanks. Approximately 40 minutes after departure, while level at 8,500 feet, she noted a gradual loss of rpm, followed by an "incipient loss of altitude." She stated that she adjusted the mixture setting and applied carburetor heat, but was unsuccessful in restoring full power. In dark night conditions, she attempted to divert to the Limon Airport, located 14 nautical miles to the east, but was unable to maintain altitude. She recalled crossing a road "at a very low altitude, and soon thereafter hit the ground" in a rough, open field. The airplane became airborne, then contacted the ground a second time. Upon impact, the aircraft nosed over. The aircraft sustained damage to the nose landing gear and the vertical stabilizer. On March 26, 1999, examinations of the engine and airframe were performed at Beegles Aircraft Services in Greeley, Colorado, with the assistance of engineering representatives from Teledyne Continental Motors and the Cessna Aircraft Company. A second inspection of the engine was accomplished on April 6, 1999, in which the engine was completely disassembled and examined. During both inspections, no mechanical engine abnormalities or discrepancies were found. 90 degree chordwise striations were observed on the cambered surface of one of the propeller blades. In addition, the spark plugs and piston domes were black in color. According to reported weather conditions at Limon, the closest weather facility located 14 nautical miles from the accident site, the temperature and dew point were 30 and 25 degrees F., respectively, with overcast ceilings at 2,500 feet. According to a carburetor icing chart (see attached), the conditions near the time of the accident were conducive to the formation of moderate to severe carburetor icing with a cruise power setting.