While the Arroyo Seco Parkway was being built and extended, the region's freeway system was taking shape. The short city-built Cahuenga Pass Freeway opened on June 15, 1940, over a month before the second piece of the Arroyo Seco Parkway was complete. In the next two decades, the Harbor, Hollywood (Cahuenga Pass), Long Beach (Los Angeles River), San Bernardino (Ramona), and Santa Ana Freeways were partially or fully completed to their eponymous destinations, and others were under construction. The centerpiece of the system was the Four Level Interchange just north of downtown Los Angeles, the first stack interchange in the world. Although it was completed in 1949, the structure was not fully used until September 22, 1953, when the short extension of the Arroyo Seco Parkway to the interchange opened. Though the common name used by the public had become "Arroyo Seco "Freeway"" over the years, it was officially a "Parkway" until November 16, 1954, when the California Highway Commission changed its name to the Pasadena Freeway.