At about 1435 Mountain time, the aircraft was substantially damaged after the Private pilot experienced a partial loss of engine power and performed a forced landing on a dirt road. There were no injuries. According to the pilot, he was in cruise flight about 10,500 feet msl along a 7000-foot-high ridge line where mountain wave action was present. The airplane began to slowly lose altitude, and efforts by the pilot to increase engine power and arrest the descent failed. The pilot then turned east, away from the ridgeline, to avoid an uncontrolled descent into terrain. Once clear of the ridgeline and any possible effects of the mountain wave, the pilot determined that the engine was capable of producing only partial power. Unable to maintain altitude, the pilot landed on a rough dirt road, causing damage to the nosewheel and left main gear, plus compression buckling and popped rivets on the wing surfaces.