On September 7, 2008, at 1245 mountain daylight time, a Cessna 210 single-engine airplane, N6515X, sustained substantial damage when the main landing gear collapsed during the landing roll at the Stevens Field Airport (PSO), Pagosa Springs, Colorado. The private pilot and passenger were not injured. The airplane was registered to and operated by the pilot. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The flight departed Santa Rosa, New Mexico, at 0950, and was destined for PSO. According to the pilot, he attempted to lower the landing gear prior to landing with the gear switch in the cockpit. The "gear would not extend down with [the] switch, therefore, I used the hand pump and it extended down 25 percent were it stopped." The pilot contacted a mechanic via cell phone and the mechanic advised him the problem could not be fixed while flying. The pilot landed the airplane with the landing gear partially retracted. During the landing, the main landing gear collapsed and the airplane exited the right side of the runway. Examination of the airplane revealed the right horizontal stabilizer and elevator were bent. On October 1, 2008, a Federal Aviation Administration inspector examined the airplane and landing gear system. No anomalies were noted with the landing gear system. The reason for the occurrence was not determined.