From the record
“The Arroyo Seco Parkway, also known as the Pasadena Freeway, is one of the oldest freeways in the United States. It connects Los Angeles with Pasadena alongside the Arroyo Seco seasonal river.”
Wikipedia article Arroyo Seco Parkway, CC BY-SA 4.0.
One of 616 National Register listings published here for Los Angeles County · listed in 2011 · category: District · built in 1940.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service