RichKenn is correct. That is the classic California Division of Highways (now CalTrans) bridge structure. I cross the current US101 bridge (not shown) every time I drive (several times a year) from the Central Coast to Orange County and return. I worked as an Engineering Aide at The Division of Highways every summer while I was attending Engineering (EE) school at USC in the late 1950's. The bridge guys were on the 6th floor, I was on the 5th floor of the Tishman Building on Wilshire Blvd (3440). in LA in those days. Great experience. But highway electrical engineering was too tame for me, I hired into Hughes Aircraft at graduation and designed CRT displays for the USN and later NATO, fun job!