Well No. 4, Pico Canyon Oil Field
Also known as: "Pico" #4; Pico Canyon,Well No. "CSO" 4
Why it's listed
Pico Canyon, in the Santa Susana Mountains north of San Fernando, holds the well where California's commercial oil industry took hold. Well No. 4, drilled by C. A. Mentry for the California Star Oil Works Company, began in July 1876 and flowed 25 barrels a day at 370 feet. Deepened to 560 feet in November 1877, it sent oil over the top of its 65-foot derrick and settled at about 70 barrels daily, the most striking production the state had yet seen. A two-inch gravity-fed pipeline linked the field to the Newhall refinery in 1879, the first of its kind in California. Union Oil Company also got its start in the canyon in 1884. The roughly 850-acre area also contains the remains of abandoned derricks, an 1880 two-story hotel for oil workers, now a residence, and an 1880 one-story school. The well still yields about a barrel of oil a day. Because of fire danger, the canyon is closed to the general public.
Significance in brief: The nomination argues that Pico Canyon was the birthplace of California's oil industry and the state's principal oil region in the 1870s and early 1880s. Well No. 4 produced 25 barrels a day in 1876 and about 70 barrels a day after being deepened in 1877, reviving a collapsing industry. Pioneers of the industry trained here, and the Union Oil Company began in the canyon in 1884.
Machine-generated summary. This summary was generated by a language model from the official nomination document and has not been reviewed line by line by an editor. It may contain errors. Check the source document before relying on any detail. Source: nomination document (PDF) · National Archives catalog entry. NRHP reference 66000212, listed November 13, 1966. Summary generated October 2026 (model claude-sonnet-5-5, prompt v1.0-2026-10-29, confidence medium).
Key facts
| Address | 9.5 mi. N of San Fernando, W of U.S. 99, San Fernando |
|---|---|
| County | Los Angeles County |
| Listed | November 13, 1966 |
| Reference number | 66000212 |
| Resource type | District |
| Architect / builder | Well drilled by C. A. Mentry for the California Star Oil Works Company |
| Areas of significance | Industry, Commerce |
| Level of significance | National |
| National Historic Landmark | Yes, designated November 13, 1966 |
| Status (as stated in the nomination) | Well No. 4 still produces about one barrel of oil a day and is California Registered State Historical Landmark No. 516. The 1880 hotel is used as a residence, and the features are little altered and well preserved. The area is closed to the public because of fire danger. |
| Acreage | 850 |
| Coordinates | 34.36941, -118.63116 (NPS GIS) |
What listing means for this property
This is a historic district. Buildings within its boundary are either contributing (they add to the district's significance) or non-contributing. Owners of contributing income-producing buildings can claim the 20% federal rehabilitation tax credit; homeowners should look at state credits. National Register districts impose no design review by themselves; a local historic district ordinance, if one exists, does (the difference explained).
General information, not legal or tax advice. Rules change; confirm with your State Historic Preservation Office or a qualified adviser.
Sources and further reading
- National Park Service, National Register of Historic Places database (snapshot May 2026), reference 66000212.
- Nomination form (PDF, National Archives) — catalog entry
- Wikipedia article (used for cross-checking only; text not reproduced here)
- Wikidata Q7191006
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.