St. Mary River Formation
| St. Mary River Formation | |
|---|---|
| Stratigraphic range: | |
Strata of the St. Mary River Formation at the St. Mary Reservoir spillway. | |
| Type | Geological formation |
| Underlies | Willow Creek Formation |
| Overlies | Bearpaw Formation |
| Thickness | up to 762 metres (2,500 ft) |
| Lithology | |
| Primary | Sandstone, shale |
| Other | Mudstone, coal |
| Location | |
| Coordinates | 49°36′N 114°06′W / 49.6°N 114.1°W |
| Approximate paleocoordinates | 49°36′N 86°30′W / 49.6°N 86.5°W |
| Region | Alberta, Montana |
| Country | Canada, USA |
| Type section | |
| Named for | St. Mary River |
| Named by | George Mercer Dawson |
| Year defined | 1883 |
The St. Mary River Formation is a geologic formation of Late Cretaceous (71.9-67 Ma) age of the Western Canada Sedimentary Basin in southwestern Alberta and northwesternmost Montana. It was first described from outcrops along the St. Mary River by George Mercer Dawson in 1883, and it takes its name from the river.
Fossils from the formation include remains of dinosaurs, as well as bivalve shells, plant fossils, and trace fossils.