Geologic Unit: Three Forks

Usage:

Three Forks Formation (ID*,MT*,UT*,WY*)
Three Forks Shale (MT*,ND*,SD*)
Three Forks Limestone (MT*,UT*,WY*)
Three Forks Group (MT*,ND*)

Subunits:

GROUP STATUS (alphabetical): Bakken Formation (MT,ND), Big Valley Formation (MT), Potlatch Formation (MT), Torquay Formation (MT,ND).
FORMATION STATUS (alphabetical): Horseshoe Hills Member (MT), London Hills Member (MT), Logan Gulch Member (MT*,WY*), Sappington Member (MT*), Trident Member (ID*,MT*,WY*).

Geologic age:

Late Devonian to Early Mississippian*

Type section, locality, area and/or origin of name:

Type section: on north bank of Gallatin River at Logan, in SW/4 SE/4 sec. 25, T. 2 N., R. 2 E., [Logan 7.5-min quadrangle], Gallatin Co., MT (Sloss and Laird, 1947; Sandberg 1962, 1965).
Standard [reference] section (subsurface): depth-interval 10,076 to 10, 310 ft, Mobil Producing Company Birdbear No. 1 well, in center SE/4 NW/4 sec. 22, T. 149 N., R. 91 W., Dunn Co., ND (Sandberg and Hammond, 1958).
Named for fine development of formation at junction of three forks of Missouri River, near Three Forks, MT (US geologic names lexicons, USGS Bull. 896, 1200).

AAPG geologic province:

Bighorn basin*
Central Montana uplift*
Great Basin province
Green River basin*
Idaho Mountains province*
Montana folded belt*
Snake River basin*
Sweetgrass arch*
Wasatch uplift
Williston basin*
Wind River basin*
Yellowstone province*