CSO-4 (Pico #4) was California's first commercially productive oil well. Spudded in early 1876 under the direction of Demetrius G. Scofield, later the first president of Standard Oil Company of California, it was completed at a depth of 300 feet on September 26, 1876, with an initial flow of 30 barrels of oil a day. Later that year, the well was deepened to 600 feet, using what was perhaps the first steam rig employed in oil well drilling in California. After this second completion, it produced 150 barrels a day and was still producing after seventy-seven years. Its success prompted the formation of the Pacific Coast Oil Company, a predecessor of Standard Oil Company of California, led to the construction of the state's first refinery nearby, marked the discovery of the Newhall Field, and powerfully stimulated the subsequent development of the California petroleum industry.
