La Mesa Model Railroad Club in downtown San Diego's Balboa Park is a nonprofit incorporated in 1962, operating one of the largest HO-scale railroad layouts in the western United States from 1649 El Prado. The club serves as a principal exhibitor within the San Diego Model Railroad Museum, maintaining a layout that replicates the 68-mile Southern Pacific and Santa Fe corridor from Bakersfield through the Tehachapi Loop to Mojave with over 30 scale miles of mainline track inside the 27,000-square-foot Casa de Balboa building. Several times per year, members convert the exhibit into a full operational simulator, running trains under 1950s-era Timetable and Train Order protocols or modern Track Warrant control practices with period-accurate signaling equipment. The layout's terrain modeling reproduces specific geological formations of California's southern Sierra Nevada range, from sedimentary cuts at Caliente Canyon to granite exposures near the pass summit—the same regional geology documented in the specimen collections at the San Diego Natural History Museum on El Prado. The club's most technically demanding work involves scratch-building accurate scale reproductions of Tehachapi Pass tunnels, bridges, and switching yards using prototype measurements and historical railroad survey data.