On September 19, 1996, at 1715 mountain daylight time, a Beech H35, N5428D, made a forced landing due to a loss of power 1 mile north of Boulder Municipal Airport (1V5), Boulder, Colorado. The private pilot and his passenger received minor injuries and the aircraft sustained substantial damage. Visual meteorological conditions prevailed for this local area personal flight conducted under Title 14 CFR Part 91 and no flight plan was filed. The flight departed 1V5 earlier in the afternoon. According to the pilot, he was at 200 feet above ground level (agl) off the departure end of runway 8, following a touch-and-go landing, when the engine lost power. He said he turned left toward an open field and conducted a forced landing with the landing gear down and 10 degrees of flaps selected. His statement said he struck a small ditch during landing roll and the nose landing gear collapsed. The aircraft slid on its nose across rocky/rough terrain and the engine separated before the aircraft came to a stop. The pilot and his passenger exited through the right rear window because the cabin door was jammed. They incurred minor injuries during impact and egress. In a telephone interview, the pilot said he had approximately 10 gallons of fuel in the left tank and had selected that tank to feed the engine a short time before power was lost. Examination of the aircraft by an FAA inspector provided verification that the left tank was selected. Due to wing damage, fuel quantity could not be verified. The FAA inspector said both propeller blades were bent rearward and bore both longitudinal and chordwise gouges and scratches. Both blades had leading edge damage and the ground contained propeller slash marks. Examination of the engine provided no evidence of mechanical preimpact failure or malfunction and examination of the fuel system provided evidence that the left tank vent was plugged with a material that had the appearance and consistency of a mud constructed insect nest. The vent tube was totally plugged and the material was not visible while conducting a normal inspection of the tube. According to available information, the aircraft had been flown 17 hours in the last 90 days, 1.7 hours in the last 30 days, and the accident flight was the first flight in the last 20 days, with takeoff and flight, until shortly before the accident, conducted with the right fuel tank selected.