On August 29, 2004, at approximately 0900 mountain daylight time, a Cessna 172S, N2099J, piloted by a private pilot, was substantially damaged during a hard landing at Tri-County Airport, Erie, Colorado. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot reported no injuries. The cross-country flight originated at Jefferson County Airport (BJC) at approximately 0845. According to the accident report submitted by the pilot, his approach speed was too high and he "ballooned." The airplane began to porpoise and impacted the nose gear. The pilot added power and initiated a go-around. At the time of the landing, the pilot was not aware that a propeller strike had occurred. The flight returned to BJC and a postflight inspection revealed that the firewall was wrinkled and the propeller was damaged.