The Stony Mountain Formation is a stratigraphical unit of Ashgill age in the Western Canadian Sedimentary Basin.

It takes the name from the community Stony Mountain, Manitoba, and was first described in the town quarry by D.B.

[2] The Stony Mountain Formation is divided in the following sub-units: [1] The Stony Mountain Formation occurs throughout the Williston Basin.

[1] It reaches a maximum thickness of 45 metres (150 ft) in the sub-surface at the Canada/United States border, and thins out towards the east, north and west.

In Manitoba, where it is exposed at the surface in the erosion belt, it has a thickness of 30 metres (100 ft).