On March 22, 2000, approximately 1630 mountain standard time, a Cessna 310C, N3311H, was substantially damaged during a forced landing near Cedar City, Utah. The flight instructor and his private pilot certificated multiengine student were not injured. The airplane was being operated by a private individual under Title 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident. The local instructional flight originated from Cedar City, approximately 1 hour before the accident. No flight plan had been filed. The flight instructor said that he shut down the right engine to practice single engine flight. Attempts to restart the engine were unsuccessful (it was later determined that the mixture control cable had failed). The pilot did not feather the right engine, and he reported that the left engine was providing insufficient power to maintain flight. The flight instructor performed a gear down landing in the rough, brush covered desert. The landing gear separated from the airplane, and the left wing leading edge and left horizontal stabilizer were damaged. The owner of the airplane said that the practice engine shut down was performed at 9,500 feet mean sea level, or approximately 3,800 feet above the terrain. He said that the practice maneuver was not initiated over a landing airfield, but that two were available within 5 miles of this location. The airplane's Owner's Manual performance section indicates that the single engine best rate of climb with the propeller feathered and the gear up would be from 50 feet per minute to 250 feet per minute, depending on altitude and outside air temperature. A manufacturer's representative said that a non-feathered propeller would reduce the rate of climb by approximately 400 feet per minute, and landing gear extended would reduce it an additional 300 feet per minute.