Driven by advances in drilling technology and high oil prices, oil companies are increasingly moving into traditionally agricultural areas like Shafter that make up one of the world’s most fertile regions but also lie above a huge untapped oil reserve called the Monterey Shale. Even as California’s total oil production has declined slightly since 2010, the output of the North Shafter oil field and the number of wells have risen by more than 50 percent.

By all accounts, oilmen and farmers — often shortened to “oil and ag” here — have coexisted peacefully for decades in this conservative, business friendly part of California about 110 miles northwest of Los Angeles. But oil’s push into new areas and its increasing reliance on fracking, which uses vast amounts of water and chemicals that critics say could contaminate groundwater, are testing that relationship and complicating the continuing debate over how to regulate fracking in California.

“As farmers, we’re very aware of the first 1,000 feet beneath us and the groundwater that is our lifeblood,” said Tom Frantz, a fourth-generation farmer here and a retired high school math teacher who now cultivates almonds. “We look to the future, and we really do want to keep our land and soil and water in good condition.”

“This mixing of farming and oil, all in one place, is a new thing for us,” added Mr. Frantz, who is also an environmentalist and is pressing for a moratorium on fracking.

Fracking is indispensable to extricating crude from the complex geological formation of the Monterey Shale, which makes up two-thirds of the United States’s shale oil reserves, oil industry officials and other experts say. If exploited, they say, the Monterey Shale could create the kind of oil boom seen in North Dakota and Texas, and could even transform California into the nation’s top oil-producing state.

Gov. Jerry Brown, a Democrat, said recently that increasing oil production could hand California a “fabulous economic opportunity,” though he said he wanted to learn more about fracking’s effects on the environment. The State Department of Conservation, which oversees the oil industry, is leading a yearlong process to establish regulations for fracking, which injects water, sand and chemicals deep into shale rock to unlock the oil and gas underground.

Meanwhile, state lawmakers have introduced nearly a dozen bills that would curtail various aspects of fracking. Environmental groups, including the Center for Biological Diversity and the Sierra Club, have sued state regulators, arguing that they have given oil companies drilling permits without subjecting them to environmental reviews. In April, after another lawsuit was filed by the groups against the United States Bureau of Land Management, a federal judge temporarily blocked exploratory drilling on 2,700 acres of public lands after ruling that the bureau had failed to review the environmental impact of fracking.

Here in Shafter, at least two farmers have sued the state and oil companies over environmental damage. A new group representing dozens of farmers, the Committee to Protect Farmland and Clean Water, is holding discussions with oil companies on drilling, fracking and compensation. The group’s lawyer, George Martin, said he could not comment because of the continuing discussions.

Rex Parris, another lawyer working with farmers, said that unlike environmental groups, most farmers do not seek to ban fracking but to regulate it strictly.
“It’s ludicrous to think that we’re going to prevent anybody from getting at that oil,” said Mr. Parris, who is also the mayor of Lancaster, a city north of Los Angeles. “The only thing we should be focusing on, because it’s the only thing we’re going to be successful at, is regulating how they get to that oil.”