Figure 1. A California oil field. Like the rest of the world, early California oil fields were quite productive but began to lose their higher volumes in mid-century. Many of these wells were sold to small independent operators who could make them profitable. Most of these fields are still active. Here, the Round Mountain Oil Field, which has produced over 100 million barrels of oil since it was spudded in 1927, making it a "giant" field. J.H. Lipps image, 1960.