Old Stuff from the Oil Fields
  (The vanishing outdoor oil museum of the San Joaquin Valley)


Tar Mines & Tunnels - Beginning in the 1860s, the first oil tunnels were dug in at Sulphur Mountain, which lies deep in the mountains that separate the San Joaquin Valley from the Santa Clara River Valley to the south. These were basically hand-dug horizontal wells, and they were the first "wells" to successfully produce the "Black Gold" of California. Twenty years ater tar mines were also dug at the McKittrick asphalt deposits to the north, and tunnels were still being driven into the sides of Sulphur Mountain. The story of the McKittrick Tar Mines is told elsewhere, what follows is the story of the tunnels.



The Sulphur Mountain area on the northern margin of California’s Ventura basin abounds in natural tar and oil seeps. Today Sulphur Mountain is part of Santa Paula oil field.

“Oil is struggling to the surface at every available point, and running down the rivers for miles and miles.” - Prof. Benjamin Silliman, Yale University, 1863

“The first thing that attracts attention is the ‘villainous smell’ of oil, the enormous deposits of asphaltum, and the oozing, bubbling, black, sluggish rivulets of petroleum. These mineral tar springs break forth from the base [of Sulphur Mountain] almost to the summit in a hundred places.”
- Mining and Scientific Press, 1872

Santa Paula oil field was discovered in 1861 when Josiah Stanford, who is shown on the left, a mining man and brother of railroad baron Leland Stanford, completed an 80-foot tunnel on the south flank of Sulphur Mountain. Using mostly Chinese labor, 54 tunnels were eventually dug by Stanford and others, most prior to 1892.

Through the 1860’s, these tunnels produced more oil than any other method in California. Generally, crude from the tunnels was hauled by horse-drawn wagon to Ventura and shipped to San Francisco for distillation into lamp and lubricating oils.

Stanford dug more than 30 tunnels at Sulphur Mountain and nearby Wheeler Canyon before moving on to other ventures. One of his tunnels is shown on the right. Twenty years later his tunnels were still producing oil, when the Union Oil Company (Unocal) came, improved some of the original tunnels, and dug twenty or so more as part of their development of the Santa Paula oil field.

Union dug the Boarding House tunnel 1,940 feet into the base of Sulphur Mountain in the spring of 1890. As shown below, company engineers used mirrors to reflect sunlight into this tunnel for lighting and alignment, a system once used by ancient Egyptians to tunnel tombs under the mountains of Libya.

Most of these tunnels were 6 feet high, 5 feet wide at the base, and 3 feet wide at the top - just large enough to accommodate a man swinging a pick. Stanford's tunnels were smaller, and simpler in construction.

Oil and water collected in a shallow ditch 8 inches deep by 18 inches wide in the tunnel floors, and a one-percent grade on the floors allowed the fluids to flow downhill to the tunnel entrances. There the fluids funneled into pipes that led to collecting tanks on the outside, where the water was separated from the oil.

Running boards laid on top of cross beams spread across the ditch allowed digging to continue while fluids ran down the ditch. One-ton mining cars, loaded with excavated dirt and rock, could then roll out of the tunnels on rails laid over the running boards.

Water zones in the tunnels were sealed off with matched tongue-and-groove redwood lumber that gave the tunnel walls needed stability. This wood siding functioned much like the wooden casing in nearby vertical oil wells

Gas vapors made tunnel digging dangerous and explosions were always imminent. Although water-laden air injected in by a water blast system could evacuate the bad air in a 560-foot tunnel in half an hour, it was difficult to adequately clear the air in longer tunnels (below).

When Union Oil had excavated the Boarding House tunnel 950 feet into Sulphur Mountain, the volatile air inside ignited with an explosion that injured four men. A second explosion a short time later killed another three. Despite these tragedies, Union finished the tunnel, extending it 1,940 feet into the mountain-deeper than most so-called “deep wells” of the day.

Thirty-two of the original fifty-four tunnels were still producing in 1997, when the photos below were taken. The tunnels at this time were connected to an oil and water gathering system maintained by the Union Oil Company. This system produced about 6 to 8 barrels of oil per day, with most of the production coming from only ten of the tunnels. The locations of many of the remaining twenty-two tunnels were unknown by this time.

These tunnels in 1997 produced about 750 barrels of fluid a day. However, rates increased significantly during high rainfall or when earthquakes open bedrock fractures previously sealed by asphalt. For example, tunnel production increased dramatically after the 6.8 magnitude Northridge earthquake of January 17, 1994 and was gauged three months later at 7,900 barrels of water per day with about 10 barrels of oil. This same quake also resulted in the appearance of an oil seep at nearby Ojai field where no seep had existed before.

Josiah Stanford's oil tunnels were California's first horizontal oil wells. The first producing vertical well in Santa Paula field was not drilled until 1875, when it was located on a tar mat in the Adams Canyon area of Sulphur Mountain. This well, called “Old Adams”, produced 2 to 3 barrels of heavy crude each day - a meager rate even back then.

Later, Adams No. 1 was drilled near “Old Adams”. This well was still producing 20 barrels a day in 1884 so Adams No. 2 was drilled 100 feet to the south. However, when No. 2 was put on pump, it drained all the oil out of No. 1. Likewise, well No. 3 drained all the oil out of No. 2, making both 1 and 2 unproductive. When Adams No. 16 was drilled in 1888, oil spouted over the derrick top to make No. 16 California’s first gusher.

The oil produced at Sulphur Mountain comes from organic-rich shales of the Miocene Monterey Formation. After expulsion from Monterey source beds, these oils migrate to the surface through fractured bedrock of the Pliocene Sisquoc Formation that is exposed in the overturned limb of the Sulphur Mountain anticline. Although bacterial action (called biodegradation), together with evaporation and oxidation, converts the seep oils into tars and asphalts, the tunnels produce crudes that average 30.3° API.

“The oil is usually struck in thin strata of sandstone, or oozes from between laminae of slaty shale; it is usually accompanied by sulphureted water. For the most part, the oil is green, but heavy black, brown, heavy and light green oils are found at no great distance from one another. Some strata penetrated by these tunnels yield much gas.” - W. L. Watts, 1897.

Tired of annual fines levied against the tunnels by the Department of Fish and Game and other California State agencies eager for revenue, Union Oil abandoned the tunnels early in 1998. The photo on the right was taken during the abandonment of the Boarding House tunnel. Now the Sulphur Mountain oil tunnels are no more.

Further Reading

Clark, Michael S., Mulqueen, Steve, Chauvel, J.P. and Nichols, John, Pacific Petroleum Geologist Newsletter, Pacific Section, AAPG, September 1998, No. 7, p. 10-11.

Lee, Patrick, 1989, Field In Trouble - Unocal still pumps oil the old way in Ventura County, Los Angeles Times (Newspaper), September 22, 1989.

Rintoul, W., 1990, Drilling through time: California Department of Conservation, Division of Oil and Gas, Sacramento, California, 178 p.

Welty, E. M. and Taylor, F. J., 1966, The 76 Bonanza: the life and times of the Union Oil Company of California: Lane Magazine and Book Company.