On August 9, 1997, at 1800 mountain daylight time, a Cessna 182P, N182WJ, nosed over during landing roll at a private airstrip near Arriba, Colorado. The private pilot and his two passengers were not injured and the aircraft sustained substantial damage. Visual meteorological conditions prevailed for this personal flight being conducted under Title 14 CFR Part 91 and no flight plan was filed. The flight departed Englewood, Colorado, at 1700. According to the pilot, he flew a standard pattern and landed with 20 degrees of flaps and 70 knots airspeed. The airstrip was grass, soft, and when the nose wheel touched down during landing roll it dug into the soft ground and the aircraft nosed over causing damage to the engine/propeller, wings, and vertical stabilizer. The pilot said he was not aware the field was soft and he was unfamiliar with the facility. The Cessna 182 Owner's Manual does not contain soft field landing procedures or any other information pertaining to soft field landings.