California Department of Public Works, pin back button

Vintage pin back button. State of California, Department of public works, Division of Highways, now called Caltrans. Measures 2 1/4" in diameter. This department was established in 1915. I presume this pin is from the 30,s or 40s. Interesting logo of a flying tire, pick, shovel and transit.Great condition for a pin of this age and type.