On October 31, 1999, about 1200 hours Pacific standard time, a Cessna 170A, N9063A, owned and operated by the pilot, ground looped during landing rollout near the El Mirage Dry Lake, about 23 nautical miles east-northeast of Palmdale, California. The airplane was substantially damaged, and the commercial pilot was not injured. The personal flight was performed under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Santa Monica, California, about 1100. During an interview with the Safety Board investigator, the pilot indicated that when he landed the local wind was light and variable. The lakebed was smooth, and no mechanical malfunctions were experienced with his airplane's flight control system. In the pilot's completed report, he indicated that his decision to land was precipitated by a "roughness in the engine," which he desired to further evaluate. Subsequently, the pilot did not report finding evidence of any mechanical malfunction with his airplane.