The following descriptions are from Ecological Subregions of the United States: Section Descrptions (McNab and Avers 1994).

Section M331A  Yellowstone Highlands

Section M331B  Bighorn Mountains

Section 331D  Northwestern Glaciated Plains

Section 331E  Northern Glaciated Plains

Section 331F  Northwestern Great Plains

Section 331G  Powder River Basin

Section M332B  Bitterroot Valley

Section M332C  Rocky Mountain Front

Section M332D  Belt Mountains

Section M332E  Beaverhead Mountains

Section M333B  Flathead Valley

Section M333C  Northern Rockies

Section M333D  Bitterroot Mountains

Section 342A  Bighorn Basin