The Bakken Oil Boom

The Bakken Formation, a rock unit buried roughly two miles beneath the surface of North Dakota and parts of Montana, is one of the largest oil deposits in the United States. The oil was known to exist for decades but was considered economically unextractable until the combination of hydraulic fracturing and horizontal drilling made it accessible beginning in the mid-2000s. The resulting oil boom transformed North Dakota from one of the poorest states in the country to one with the fastest-growing economy in the nation, nearly doubling the state's population in the western oil patch region in under a decade.

Source: Wikipedia