On February 24, 1994 at 0942 mountain standard time, a Mooney M20J, N201SX, was substantially damaged during a forced landing near Gallup, New Mexico. The private pilot was not injured. Visual meteorological conditions prevailed for the personal flight. The pilot stated in the enclosed pilot/operator report that while in cruise flight at 8,500 feet MSL, he heard a "pop-like" sound coming from the engine, immediately followed by a severe engine vibration. The pilot added that the engine lost power and he proceeded to shut down the engine. A forced landing to a snow covered open field was performed. The pilot elected to land with the landing gear extended. During the landing roll the right main landing gear collapsed after it collided with tree stump. Post accident examination of the engine revealed that the exhaust valve for the number 3 cylinder failed, resulting in the total loss of engine power.