On July 3, 2013, about 2000 mountain standard time, a Cessna T210K, N272EF, sustained substantial damage when the left main landing gear collapsed while on landing roll at Phoenix-Mesa Gateway Airport, Phoenix, Arizona. The private pilot, the sole occupant of the airplane, was not injured. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the personal cross-country flight, which had originated at 1825 from Falcon Field Airport, Mesa, Arizona. A flight plan had not been filed. The pilot reported that he had put the landing gear down, but the left main landing gear down-and-locked light did not indicate that it was safely locked. After several attempts to get the left main landing gear safely down and locked, the pilot landed the airplane, and the left main landing gear collapsed. The left horizontal stabilizer and elevator were bent and wrinkled. In the presence of a Federal Aviation Administration inspector, on August 22, 2013, the left main landing gear actuator assembly was disassembled. A broken gear tooth from the end to the piston assembly was found. This tooth was responsible for the final "down lock" of the left main gear. The assembly operated properly in the "up and locked" position, which the pilot verified occurred with each cycling of the landing gear. The failed tooth was not made available for further examination and the failure mode was not determined.