The pilot and passenger departed in an 85-horsepower, single-engine airplane from an airport with a density altitude that was later calculated to be about 8,666 feet. When the airplane was approximately 300 feet above ground level, the airplane experienced a loss of lift. Unable to maintain altitude, the pilot selected a dirt road as a possible landing site; however, the airplane impacted terrain before reaching the road. The airplane came to rest in an upright position and the pilot and passenger were able to exit the airplane unassisted. An examination of the engine revealed no preimpact anomalies.