On November 16, 2000, at 1540 hours Pacific standard time, a Cessna 210K, N8118G, lost engine power and made a forced landing near Oxnard, California. The airplane sustained substantial damage; however, the certificated private pilot, his passenger, and two dogs were not injured. The airplane was being operated by the pilot/owner as a personal flight under 14 CFR Part 91 when the accident occurred. The flight originated from the Chino, California, airport at 1505. Visual meteorological conditions prevailed at the time and no flight plan was filed. The pilot reported that he had begun his descent from his en route cruise altitude of 10,500 feet mean sea level (msl) when, after descending about 400 to 500 feet, he felt a minor concentric vibration. He immediately checked engine oil pressure and fuel mixture, and determined that both were within limits. Shortly thereafter, the vibration increased in magnitude and he reduced the throttle. At this time he also richened the mixture, switched fuel tanks, and tried to adjust the propeller pitch in hopes of somehow reducing the vibration. The pilot declared an emergency to Los Angeles center and was given a heading of 140 degrees to the nearest airport, which was at Oxnard. After turning to the new heading, the engine quit. He informed center that he would not be able to reach Oxnard. About 5,200 feet msl, the pilot saw an open area and set up a normal traffic pattern approach. When he was sure that landing was assured, he attempted to lower his landing gear and applied full flaps. He estimated his final approach was a little fast, about 90 to 100 knots. He attributed the higher speed to the fact that he dove the airplane slightly since it was still too high during the turn to final. As the airplane touched down, the pilot applied the brakes. The airplane skidded about 300 to 400 feet before striking a perimeter fence and a tree. As the airplane struck the tree, it yawed about 90 degrees to the right and came to a stop. The airplane had its engine replaced the previous May. The new engine was a factory remanufactured Continental IO-550. It replaced the original Continental IO-520, and its installation was authorized under a supplemental type certificate (STC). The engine was taken to Teledyne Continental Motors, the manufacturer, in Mobile, Alabama, for disassembly and inspection. The engine was found to have a broken cam gear.