Madison Group
The Madison Limestone is a thick sequence of mostly carbonate rocks of Mississippian age in the Rocky Mountain and Great Plains areas of the western United States. The rocks serve as an important aquifer as well as an oil reservoir in places. The Madison and its equivalent strata extend from the Black Hills of western South Dakota to western Montana and eastern Idaho, and from the Canada–United States border to western Colorado and the Grand Canyon of Arizona.
| Madison Limestone | |
|---|---|
| Stratigraphic range: | |
Thrust segment of the Madison Limestone, Sun River canyon, Montana | |
| Type | Geological formation |
| Underlies | Big Snowy Group |
| Overlies | Bakken Formation (Three Forks Group) |
| Thickness | up to 2,100 feet (640 m) |
| Lithology | |
| Primary | Limestone |
| Other | Shale |
| Location | |
| Region | South Dakota, Montana, Idaho, Colorado, Arizona, Alberta, Saskatchewan, Manitoba, Utah |
| Country | United States Canada |
| Type section | |
| Named for | Madison Range |
| Named by | A.C. Peale, 1893 |
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