| Blue Mountain Formation | |
| Period: | Late Ordovician |
| Type: | Geological formation |
| Prilithology: | Shale |
| Otherlithology: | Limestone, siltstone |
| Region: | Southern Ontario, |
| Country: | Canada |
| Subunits: | Rouge River Member |
| Overlies: | Lindsay Formation |
| Thickness: | Up to 76m (249feet) |
| Namedfor: | Blue Mountain |
| Namedby: | W. A. Parks |
| Year Ts: | 1928 |
The Blue Mountain Formation (previously the Whitby Formation) is a geological formation of Upper Ordovician age (Maysvillian Stage), which outcrops in Ontario, Canada from Nottawasaga Bay southeastward to the Toronto area.[1] [2]