California opens its first freeway, the Arroyo Seco Parkway.

California is a state in the Western United States that lies on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with the Mexican state of Baja California to the south. With almost 40 million residents across an area of 163,696 square miles (423,970 km²), it is the largest state by population and third-largest by area.

A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway, and expressway. Other similar terms include throughway or thruway and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highways with somewhat less isolation from other traffic.

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. Mostly opened in 1940, it represents the transitional phase between early parkways and later freeways. It conformed to modern standards when it was built, but is now regarded as a narrow, outdated roadway. A 1953 extension brought the south end to the Four Level Interchange in downtown Los Angeles and a connection with the rest of the freeway system.