FELLOWS, Calif. — Secure in this state’s history and mythology, the venerable Midway-Sunset oil field near here keeps producing crude more than a century after Southern California’s oil boom. Many of its bobbing pump jacks are relatively short, a telltale sign of the shallowness of the wells and the ease of extracting their prize.

But away from this forest of pump jacks on a flat, brown landscape, a road snakes up into nearby hills that are largely untouched — save for a handful of exploratory wells pumping oil from depths many times those of Midway-Sunset’s. These wells are tapping crude directly from what is called the Monterey Shale, which could represent the future of California’s oil industry — and a potential arena for conflict between drillers and the state’s powerful environmental interests.

At one such exploratory site, tall pump jacks stood above two active wells on a small patch of federal land. For now, the operator, Venoco, has been storing the oil in two large tanks. But construction is scheduled to start soon on pipelines, and more wells are planned.

Comprising two-thirds of the United States’s total estimated shale oil reserves and covering 1,750 square miles from Southern to Central California, the Monterey Shale could turn California into the nation’s top oil-producing state and yield the kind of riches that far smaller shale oil deposits have showered on North Dakota and Texas.