On November 20, 2002, about 1610 mountain standard time, a Cessna T210L, N59132, nosed over during a precautionary off airport landing near Williams, Arizona, after experiencing smoke in the cockpit. The airplane was destroyed by impact and fire. Sierra Aviation LLC was operating the airplane under the provisions of 14 CFR Part 91. The airline transport pilot and one passenger sustained minor injuries. The positioning flight departed Prescott (PRC), Arizona, about 1550, en route to St. George Municipal Airport (SGU), St. George, Utah. Day visual meteorological conditions prevailed, and no flight plan had been filed. In a written statement, the pilot stated that the flight departed from PRC for Gowen Field (BOI), Boise, Idaho, with a planned fuel stop at SGU. Approximately 10 minutes after departure, the pilot and his passenger smelled smoke. The pilot opened the vents and turned off the avionics master switch and master switch. The smoke increased. The pilot reduced power and began descended. The passenger crawled to the back seat and pushed the doors open with his feet. The smoke continued to increase. The pilot stated that he used the master switch momentarily to extend the flaps to 20 degrees and to extend the landing gear. The landing gear would not extend. He attempted to emergency extend the gear, but the gear still would not extend. The pilot then told the passenger to stay in the rear seat and to fasten his seatbelt. He turned off all electrical switches and turned into the wind. The pilot made a gear up landing in a clearing with near zero visibility due to smoke. The airplane nosed over and came to rest inverted. The pilot and passenger "saw flames" and exited the airplane. The airplane continued to burn for over an hour. A Federal Aviation Administration (FAA) inspector examined the airplane, but was unable to determine the origin of the fire due to the extensive fire damage.