I'm a geologist who's been researching unconventional oil plays, such as the Bakken, for the last two years. Unfortunately, the Bakken is one play I haven't thoroughly researched yet. However, a simple google search using Bakken Formation quickly found this image.
I'm certain there are images that can define the area better.
BTW the Bakken Formation is found in the Williston Basin, also outlined on this map. As the price of oil goes up there's a chance the area marked Extent of Bakken Formation will expand outwards.
Steve
