A Montana judge has sentenced the leader of an interstate drug ring to 20 years in prison for his role in a trafficking operation that stretched from western Washington to the Bakken oil fields of the Northern Plains.

In a sentencing hearing Friday, U.S. District Judge Susan Watters described Robert Farrell Armstrong as a long-time criminal and a danger to society.

In a deal with prosecutors, the Moses Lake, Washington, man pleaded guilty in January to a single count of possession of methamphetamine with intent to distribute.

Watters said Armstrong preyed upon addicts in the Montana-North Dakota oil patch to build up a network of dealers and armed enforcers.

Authorities say the drug ring moved as much as a pound of meth a week before it was busted up last year.