BILLINGS (AP) — An investigation into drug crimes in the Bakken oil patch have led to the arrests of 11 people linked by authorities to a ring that trafficked methamphetamine from southern California to the Northern Plains, according to court documents and the U.S. Attorney’s Office.

Authorities said Friday the defendants will face drug conspiracy charges in Montana.

The defendants include four Montana residents, three from Los Angeles and four from Taft, Calif.

A formal indictment has not yet been filed.

FBI affidavits filed in several of the cases described some of the defendants as shipping more than 2 pounds of meth from California for distribution in Billings, Roundup, and Rapid City, S.D,. earlier this year.

None of those cities are in the Bakken region, but authorities say they can serve as staging points to move drugs into the oil patch.

Each of the 11 faces a single count of conspiracy to possess meth with intent to distribute, which carries a potential penalty of life in prison and a fine of up to $10 million upon conviction. Calls to defense attorneys were not immediately returned Friday.

The arrests mark at least the third major trafficking ring to be targeted by state and federal law enforcement as authorities crack down on drug sales driven by dealers wanting to profit off the oil money flowing into the region.

More than 20,000 people have poured into eastern Montana and western North Dakota since crude production began its meteoric rise in 2008. Tens of thousands more are expected in the next several years as the boom continues.

Local law enforcement agencies have been overwhelmed with the rise in criminal offenses, prompting federal and state agencies such as the Montana Division of Criminal Investigation to move more resources into the oil patch.

U.S. Attorney Mike Cotter said 59 people have been indicted on drug charges since the multi-agency “Project Safe Bakken” crackdown began, and at least 70 more indictments are expected in the next 12 months.

“What we’re doing in the Bakken with state and local agencies is a constant battle,” Cotter said. He declined to comment on the latest arrests.

In October, a dozen people tied to a ring that imported meth from Washington state into eastern Montana was broken up. The defendants have all pleaded guilty to federal charges.

Since July, authorities in North Dakota have charged 26 people with crimes linked to a conspiracy to sell heroin and other drugs on an Indian reservation in the heart of the oil patch. The ring had connections to a national drug trafficking organization seeking to make inroads in the Bakken, authorities said.