Geologic Unit: Jefferson

Usage:

Jefferson Formation (ID*,MT*,UT*,WY*)
Jefferson Dolomite (ID*,MT*,UT*,WY*)
Jefferson Dolostone (ID*,MT*,UT*,WY*)
Jefferson Limestone (ID*,MT*,UT*,WY*)
Jefferson Group (subsurface of MT*,ND*,SD*,WY*)

Subunits:

GROUP STATUS (alphabetical): Birdbear Formation (MT*,ND*,SD*), Duperow Formation (MT*,ND*,SD*), Nisku Formation (ND).
FORMATION STATUS (alphabetical): Birdbear Member (ID*,MT*,WY*), Coopers Lake Limestone Member (MT), Glenn Creek Shale Member (MT), Hyrum Dolomite Member (UT*) or Hyrum Member (ID*), Lone Butte Member (MT), Samaria Limestone Member (ID,UT), Spotted Bear Limestone Member (MT), White Ridge Limestone Member (MT).

Geologic age:

Middle to Late Devonian*

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

Notable exposures in hills on both sides of Missouri River just below junction of the Three Forks of the Missouri, and on both sides of the Jefferson a few mi above its mouth, in Three Forks quadrangle, southwestern MT (Peale, 1893).
Type section: on north bank of Gallatin River at Logan, in S/2 SE/4 sec. 25, T. 2 N., R. 2 E., Gallatin Co., southwestern MT [approx. Lat. 45 deg. 53 min. 25 sec. N., Long. 111 deg. 25 min. 30 sec. W., Logan 7.5-min quadrangle] (Sandberg, 1962, 1965).

AAPG geologic province:

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