The Lost Hills oil field owes much of its production today to hydraulic fracturing. Photos by Andrew Alden

"Fracking," the ugly nickname for a common oilfield practice, is a rising concern in many places. What about California? Appropriately for a high-tech state, all kinds of advances in underground techniques have been used here. How safe are they? Hard to say.

Working with underground spaces means entering a dynamic environment. California oilfield operators learned that very early in ways that would horrify us today. A century ago, drillers would sometimes tap a highly overpressured oil pool and cause a gusher. The worst of these was the Lakeview gusher, a blowout that began in the spring of 1910 between Taft and Maricopa and lasted more than a year. (The scene today is marked by a plaque.) It ruined the California oil industry for a while—not because of environmental degradation or public revulsion or a government crackdown, but because the flood of oil made the price of crude collapse. Let me put it this way: the problems we have today from oilwell technologies aren't like they used to be.

Site of the Lakeview gusher north of Maricopa. A hundred years later, the ground is still paved with asphalt.

Fracking (hydraulic fracturing) is a way to open up deep rocks by pumping liquids down a borehole at high pressure. The idea is to make a lot of little cracks in tight rocks so the trapped oil can flow out. In the old days, well operators in the Los Angeles basin would goose a fading well by pumping down the crude oil already in the borehole. Today fracking involves water mixed with a little sand, which washes into the new cracks and jams them open. It's widely performed in California to keep old oilfields producing.

You have to pump the fracking water back out before you can extract the oil. Most of the time you can pump it down somewhere else to backfill the space that used to hold the oil, a technique called water injection. The industry learned that about 50 years ago when sinking ground caused shallow earthquakes. The huge Wilmington oil field under Long Beach had six damaging earthquakes between 1947 and 1961 before water injection made them stop.

Today oilfield earthquakes are not a problem in California. Disposal of excess fracking water is our dirty secret. Fracking water gets tainted from its exposure to the oil and natural brines down there, plus it's also mixed with various ingredients to help with the downhole chemistry. Water injection takes care of a lot of dirty fracking water, but the rest needs to be dealt with somehow. In the old days it was dumped on the ground or poured into ponds to evaporate, without much care. Today . . . well, nobody has been keeping track of the industry.

The state government's Division of Oil, Gas and Geothermal Resources (DOGGR) claims to be regulating fracking, but when the state Senate Committee on Natural Resources and Water inquired early last year, the agency had no data to supply. This was a year after DOGGR had gotten extra money, money it had asked for, to develop fracking regulations. The agency now says on its website that it "only has limited information about the use of the practice."

The Environmental Working Group recently compiled what it could find on California fracking and DOGGR's role in overseeing it and issued a critical report called "California Regulators: See No Fracking, Speak No Fracking." The title makes its message clear, and even though I am allergic to activist overstatement of all kinds, I found its factual contents worth heeding. Now the state legislature is considering several bills to encourage more disclosure of fracking; one of them, SB 1054, would require neighboring property owners to be notified of fracking 30 days in advance. The issue is alive, and the legislative sumo match is underway. But the people's watchdog is sitting it out, leaving the fray to lawmakers and lobbyists.

Cattle range in the Big Blue Hills just a few miles from the Harris Ranch feedlot. Photos by Andrew Alden

Driving Interstate 5 through the Central Valley, I find something to like on every mile except one: the smelly vicinity of the Harris Ranch feedlot north of Coalinga. This is how you can avoid it and enjoy some geology for an hour or so.

Assuming you're heading south, the key is to get off of I-5 about 10 miles before the feedlot, at the Route 33 North/Derrick Avenue exit. Think of Derrick as old Route 33, because 33 actually joins I-5 here for a few miles before exiting to the right and meeting Derrick again farther south. See if that makes sense on the geologic map below. This side trip follows 33 into Coalinga and then straight east to the interstate, crossing some interesting structure and a couple of oil fields.

Significant map units from oldest to youngest: Ku, upper Cretaceous marine rocks; Ep, Paleocene marine rocks; E, Eocene marine rocks; M and Mc, Miocene rocks; P; Pliocene rocks; QPc, Pliocene-Pleistocene nonmarine rocks; Q, modern and recent sediment; Qoa, Quaternary river terraces. Magenta lines mark structural arches and troughs, with arrows indicating dips of adjoining strata and plunge of the feature's axis

Derrick Avenue runs for a while through orchard lands parallel to I-5, crossing it twice. Hang in there: it eventually veers away into the Big Blue Hills, as these foothills of the Coast Range are called, out of earshot of the big freeway and smellshot of the big feedlot.

The country here is rolling semidesert, marginal rangeland. The ground underfoot was muddly seafloor for many millions of years, until quite recently in geologic time, around 5 million years ago. Then slow compression across the San Andreas fault raised the Coast Range, buckling these sediments into arching folds. The upward-buckling folds are called anticlines, scientific Latin that means "sloping apart." (Downward-warping troughs, like the one running the length of the Central Valley's western edge, are called synclines.)

Erosion then got to work on the anticlines, peeling away their youngest layers and exposing progressively older rocks. Meanwhile underground, oil and gas worked their way uphill in the newly tilted strata to collect along the center of the nearest anticline. The area around Coalinga, including this part of the Big Blue Hills, is the northern edge of the California oil patch. Now maybe Derrick Avenue's name makes more sense.

Derrick Avenue meets Route 33 again, and you'll turn right on it—going left takes you straight to the stinky feedlot. The road then crosses Anticline Ridge and the heart of the Coalinga Oil Field. Take the Shell Road turnoff if you like where Route 198 comes in; both ways lead to town.

Wells of the Coalinga Oil Field. Photo courtesy Wikimedia Commons

The Coalinga field is the largest of several around here. It was the first great oil district in the Central Valley and remains productive today using enhanced recovery techniques.

Courtesy California Division of Oil, Gas & Geothermal Resources

The oil-bearing hills give way to Pleasant Valley, a syncline filled with young sediment that's occupied by farmland, a state prison, and the town of Coalinga. There are places in town to take a break and find a snack, not to mention the local attraction the R. C. Baker Memorial Museum. Then follow Route 33 out of town again.

It's possible to make Coalinga the start of an extended trip through the oil patch—just follow Route 33 south where it turns right. But to end this side trip, stay on the straightaway, crossing the anticline one last time in the low Guijarral Hills and its moribund oil field to reach the freeway, which is already in progress.

Wikipedia calls this the last working pump in the Guijarral Hills Oil Field. Wikimedia Commons photo

Also still in progress is the rise of the Coast Range. On the afternoon of 2 May 1983, Anticline Ridge jolted up another foot or so in a magnitude 6.4 earthquake. I was sitting in Menlo Park at the time and remember well its ominous slow roll, the sign of a big one somewhere far away.

Oil wells creak in the Bakersfield twilight. Petroleum is not confined to Southern California and Central Valley; we have it in the Bay Area too. Photo by Andrew Alden.

Norma Desmond, the washed-up movie star of Sunset Boulevard, had some memorable lines. One of them was, "I've got oil wells in Bakersfield, pumping pumping pumping." We think of our petroleum as a Southern California thing, or at least no closer than the Great Valley. But petroleum—oil and gas, or both—is widespread around the state, including the Bay Area.

It wasn't just gold, water and agricultural soils that made California rich. Petroleum is one of our greatest natural assets, and the state still ranks fourth in oil production behind Louisiana, Texas and Alaska. While the forests of derricks that once dotted Los Angeles are now subdued and disguised, the Central Valley is still a proud petroleum region, with gas fields in the Sacramento Valley and oil fields in the San Joaquin Valley.

The oil and gas fields of the Central Valley intrude into the Bay Area from the Delta as far as Concord and the Suisun Bay to its north. Gas was produced from the hills north of Concord in the 1960s, and today the old Los Medanos gas field is used by PG&E for storage.

Photo (c) 2007 Andrew Alden

Before petroleum exploration became high-tech, the best way to find oil and gas was to look for natural seeps. An oily sheen on a stream, trickles of tar from a sunny sea cliff, and persistent odors like kerosene are typical signs. These are more common than most people think. Much rarer are actual tar flows like those at Carpinteria Beach near Santa Barbara.

Photo (c) 2010 Andrew Alden

Oil seeps were discovered near Half Moon Bay and in the Santa Cruz Mountains in the 1800s. Asphalt and tar sand were mined from these areas for the streets of San Francisco.

Natural asphalt from the McKittrick tar seep. Photo by Andrew Alden

Later, conventional exploration opened up four districts of producing wells in the San Mateo Peninsula: the Half Moon Bay, La Honda and Oil Creek fields still yield oil today. The Moody Gulch field, which started as a tar pit in 1878, was shut down in 1960 and is now under Route 17.

Photo by Les Magoon, U.S. Geological Survey

Elsewhere in the Bay Area, oil and gas have been produced in Petaluma, Pinole and Livermore. Oil was reported in the Caldecott Tunnel excavations, which is to be expected as the tunnel penetrates our local piece of the Monterey Formation, a petroleum source rock of great extent.

Oil and gas are called fossil fuels, but maybe a better concept is that they are geological compost. They are the bodies of dead plankton, trapped in the mud with no oxygen to consume them. Instead their living substance breaks down and is transformed into simpler hydrocarbon compounds.

The simplest and lightest of these is methane, and that's refined and sold to us as "natural gas." But actual natural gas, the stuff bubbling up in tar pits, is a mixture of compounds. It won't smell like the gas in your stove—that smell is the odorant butyl mercaptan. It's more like the smell of crude oil—a tantalizing, sweeter version of your local gas station. If you don't know how crude oil smells, take a side trip to the oil fields on your way south, like this one just off Interstate 5 at Lost Hills.

Lost Hills oil field. Photo (c) 2010 Andrew Alden

The U.S. Geological Survey has a wealth of material on California's oil and gas seeps at walrus.wr.usgs.gov/seeps.

You may listen to the "Chevron's Plans" Radio report online, as well as find additional links and resources.

Amy Standen is a Reporter for QUEST and Radio News at KQED-FM.