Cadomin Formation, Geological formation in Alberta, Canada

The Cadomin Formation is a conglomerate layer of Early Cretaceous age in the Western Canada Sedimentary Basin, extending from southeastern British Columbia through western Alberta to northeastern British Columbia. It consists of well-rounded pebbles, cobbles and boulders of white, grey and green chert and white and grey quartzite in a quartzose sand matrix, cemented by silica. It forms prominent outcrops, with thickness ranging from 1 to over 170 metres.

The Cadomin Formation was named after the mining town of Cadomin, an acronym of "Canadian Dominion Mining". It is Early Cretaceous (Barremian to Aptian) in age and forms the basal unit of the Bullhead Group in northeastern British Columbia and of the Blairmore Group in Alberta. Its deposition followed a long period of uplift, exposure and erosion of older strata, and it rests unconformably on units such as the Fernie, Nikanassin, Minnes or Kootenay formations.

The name Cadomin comes from the mining town of Cadomin, an acronym of "Canadian Dominion Mining". The formation was long called the "coal conglomerate" because its hard, silica-cemented beds served as a marker horizon for locating the coal seams of the Mist Mountain and Gething formations. Outcrops near Cadomin, Alberta, are the type locality.

The type locality is at outcrops near Cadomin, Alberta, where the formation is exposed in the foothills of the Canadian Rockies. It can be traced from the Canada–US border to the Peace River region, over 1,000 km. The resistant conglomerate forms prominent ledges, and thickness varies from 1 m to over 170 m.

The oldest dinosaur skeletal fossils in Alberta, and anywhere in Canada west of Nova Scotia, come from the Pocaterra Creek member at the base of the Cadomin Formation. They belong to a polacanthid ankylosaur, an armoured plant-eater; unattributed turtle material was found at the same locality. The formation itself is otherwise not fossiliferous.