Originally started as a WPA flood control project, the Arroyo Seco Parkway—also known as the Pasadena Freeway—is considered one of the most important roads in American history. Built by the WPA and PWA (in conjunction with local agencies) and mostly completed by 1940, it was the first freeway west of the Mississippi. At the dedication, California Governor Culbert Olson stated, "It takes courage to do a thing the first time, no matter how simple and obvious it may appear after it is done. And this, fellow citizens, is the first Freeway in the West."

Designed in the parkway tradition, it features lush landscaping, windy curves and highlights the unique geographical features of Southern California, including views of the San Gabriel Mountains. It was also practical, becoming the initial stretch of road for the well-known (and, now, much maligned) Los Angeles freeway system. Today, it's still in nearly the same configuration it was in 1940 and is a American Society of Civil Engineers Historic Landmark.