The airplane was destroyed when it collided with mountainous terrain at approximately 0930 Mountain time during descent from cruise altitude. Visual conditions prevailed at the accident scene; the Private pilot was fatally injured. A witness about two miles from the accident site heard the approaching airplane; its engine was “sputtering.” He did not see the airplane but heard an explosion. He ran to a clearing and saw a fire on the mountainside near the peak. Preliminary on-site investigation revealed the airplane struck the mountain in a wings-level, nose slightly low attitude, then slid downhill approximately 75 feet. The airplane and surrounding vegetation caught fire and eventually burned itself out. The landing gear and flaps were both retracted.