The pilot departed on a 1 hour and 50 minute cross country flight with approximately 30 gallons of fuel in each wing tank (approximately 27 gallons usable fuel per side). The flight was uneventful until he started a descent to land from 8,000 feet to 3,000 feet, when the engine made "two pops" and "quit." The pilot said there was no engine roughness "it just stopped." He made several attempts to re-start the engine, but was unsuccessful. The pilot declared an emergency and landed in a field. Upon landing, the nose gear dug into the dirt and separated from the airplane. The right wing rear spar had also fractured during the landing; however, both wing fuel tanks were undamaged. Approximately one-quart of fuel was drained from the left wing tank, and the right wing tank contained approximately 30 gallons of fuel. The pilot could not recall what the position of the fuel selector was at the time of the power loss. Examination of the engine and fuel system revealed no mechanical anomalies.