Riverside Motorsports Park was a proposed 1,200-acre (5 km2), motorsports-themed family entertainment park to be built in Merced County, California. The name "Riverside Motorsports Park" was not derived from its location (which was miles from the nearest river). Instead, the name was derived from the configuration of the park's 3-1/2 mile Road Course, which would have replicated, as closely as possible (given current track safety requirements), the road course at the Riverside International Raceway (Riverside, California) that closed in 1989. The RMP site was next to the former Castle Air Force Base, which is now operated as Castle Airport.