Southwestern Canada was located in the tropics during the Cambrian and Ordovician, with the western part of the craton of the Canadian shield covered by shallow seas. Carbonates accumulated in these warm seas in the Middle Cambrian–Middle Ordovician, together with terrigenous detritus carried by rivers from the craton to the east. Thick carbonates developed in the outboard parts of the carbonate platform, facing the deeper waters of the bordering oceanic trough; thicknesses total some 4000 m (13,000 ft). The outboard edge of the carbonate platform varied in position with time. In the south, for most of the Middle Cambrian–Middle Ordovician, the edge was located just west of the present Alberta-British Columbia boundary as the Kicking Horse rim, the site of submarine topography and spectacular changes of facies from shallow-water carbonates to slope deposits and basinal sediments of mudrocks and clastics.

Nine grand cycles can be recognized within the Middle Cambrian to Middle Ordovician carbonates, with the top of each heralding a drop of sea level and a corresponding transgression. The formations of the carbonate platform thin to the east and northeast and have been beveled by several unconformities so that the stratigraphic package is only about 600 m (2000 ft) thick in the subsurface of southern Alberta and the northern Williston Basin.