CSO Well Number 4

The first commercially successful oil well in the western United States and also the longest-​running oil well in the world up until 1990. I wouldn’t make a separate trip to view it unless you’re an oil history buff. If your visit includes Mentryville and Pico Canyon trail then it’s well worth the trip.
California Historical Landmark No. 516 WELL, CSO 4 (PICO 4) —
The inscription reads:
On this site stands CSO-​4 (Pico No. 4), California’s first commercially productive well. It was spudded in early 1876 under direction of Demetrious G. Scofield who later became the first president of Standard Oil Company of California, and was completed at a depth of 300 feet on September 26, 1876, for an initial flow of 30 barrels of oil a day. Later that year, after the well was deepened to 600 feet with what was perhaps the first steam rig employed in oil well drilling in California, it produced at a rate of 150 barrels a day — it is still producing after 77 years (1953). The success of this well prompted formation of the Pacific Coast Oil Company, a predecessor of Standard Oil Company of California, and led to the construction of the state’s first refinery nearby. It was not only the discovery well of the Newhall Field, but was a powerful stimulus to the subsequent development of the California petroleum industry.
Location: On W Pico Canyon Rd, 3.3 mi W of I-​5, Newhall

California Historic Landmark number 516. This was California’s first commercially productive oil well. You’ll have to walk to the site from Mentryville.