| Chadron Formation | |
| Type: | Geological formation |
| Age: | Late Eocene ~ |
| Period: | Eocene |
| Prilithology: | Fine grained clastic rocks |
| Otherlithology: | Tuff, Sandstone |
| Namedfor: | Chadron, Nebraska |
| Region: | Nebraska, Wyoming, North Dakota, South Dakota |
| Country: | United States |
| Unitof: | White River Formation |
| Underlies: | Brule Formation |
| Overlies: | marine indet. |
Chadron Formation is a rock formation in North Dakota, South Dakota, northwestern Nebraska, and eastern Wyoming. It is named after the town of Chadron, Nebraska. It was mapped out by Carl Vondra in the 1950s.[1]