La Mesa (lə māˈsə) [key], city (1990 pop. 52,931), San Diego co., S Calif., a suburb of San Diego; inc. 1912. It is a retail center and a popular residence for upper- and middle-income professionals in the San Diego area. There is light manufacturing. Points of interest include the McKinney House, the Pacific Southwest Railway Museum, and nearby Mt. Helix, with its impressive view of the surrounding region.