The Arctomys Formation is a stratigraphic unit of late Middle Cambrian age.

[3] It was named for Arctomys Peak near Mount Erasmus in Banff National Park by Charles Doolittle Walcott in 1920.

[4] The Arctomys was deposited along the western shoreline of the North American Craton during late Middle Cambrian time.

Sedimentary structures include mudcracks, ripple marks, and casts of salt crystals.

It thickens northward from White Man Mountain to a maximum of 336 metres (1,100 ft) at Mount Robson.