The pilot was 1 hour 24 minutes into the flight at a cruise altitude of 8,000 feet when he reported to Air Traffic Control (ATC) that he had lost engine power. He was approximately 12 miles from the closest airport at a field elevation of 2,693 feet, and was provided vectors to that airport. He radioed ATC 3 minutes later advising them that he was descending at a rate of 600-700 feet per minute and was unsure whether he could make it to the airport. One minute later, he contacted ATC and advised that he was going to try to land on the highway. There was no further radio communication. A witness reported seeing the aircraft without engine power descending to the south in a steep angle. She reported that the aircraft made a sudden left turn and fell to the ground. The wreckage was located 3.5 miles north of the airport where it came to rest on a dirt road. Examination of the airplane did not disclose evidence of mechanical malfunction.