On July 11, 1998, approximately 0515 mountain daylight time, N121GD, an Overton Mustang M-II, was destroyed when it collided with wires and impacted terrain near Hillsdale, Wyoming. The private pilot, the sole occupant aboard, was seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under Title 14 CFR Part 91. The flight originated at Erie, Colorado, approximately 0440. In a telephone interview from his hospital bed, the pilot said the engine began to "miss" and "run rough." He sighted a road below and descended to assess its suitability for an emergency landing. The airplane struck wires that crossed the road, impacted the roadway, then collided with a bridge. In his accident report, the pilot said the flight was to be a local personal flight "with no particular destination in mind." He heard a "slight hesitation or miss" in the engine and increased power slightly. The engine gauges registered normal and the engine seemed to "smooth out." He descended to survey a road "as a possible landing spot in case of an engine failure." He felt the airplane strike something and shudder, then heard a loud rumbling noise. The airplane then struck the ground.