Hoodoos near Drumheller, Alberta. The capping stones of harder ironstone slow erosion on the columns beneath them, leaving pillars standing while the surrounding material is washed away. Photo: Kevin Philipson / Wikimedia Commons / CC BY-SA 4.0.
What makes badlands
Badlands form where soft sedimentary rock — typically mudstone, shale, or poorly cemented sandstone — is exposed to rapid erosion by water and wind. The term "badlands" was applied historically because the terrain was difficult to cross on foot or horseback: steep, unstable slopes, minimal vegetation, and no reliable surface water. In Alberta, the badlands occupy the coulees and valley walls along the Red Deer River from approximately Drumheller to the Saskatchewan border.
The rock exposed in the Drumheller Valley is predominantly from the Horseshoe Canyon Formation and the underlying Bearpaw and Belly River formations — all Late Cretaceous in age, deposited roughly 65 to 75 million years ago. At that time, Alberta sat on the margin of a shallow inland sea (the Western Interior Seaway) and adjacent coastal plains and river deltas. The alternating layers of marine shale, terrestrial mudstone, sandstone, and coal seams visible in the valley walls record the fluctuating shoreline of that sea.
How hoodoos form
A hoodoo is a tall pillar of soft rock protected from erosion by a capstone of harder material — typically a boulder of resistant sandstone or ironstone resting on a column of softer mudstone or shale. The cap sheds water to the sides, protecting the material immediately beneath it while the surrounding terrain erodes away. Over time, the pillar is left standing while the hillside retreats, giving the formation its characteristic mushroom-like profile.
Drumheller's hoodoos are among the most photographed in Canada, reaching 5 to 7 metres in height. They are not permanent features: once the capstone erodes or falls, the column beneath it weathers rapidly. New hoodoos form as erosion continues to undercut and isolate protected columns from the valley walls. The landscape is actively changing at a rate perceptible over years, not millennia.
Iron-rich concretions — rounded nodules of ironstone that formed within the sediment before lithification — are common capstones. Where softer layers are interbedded with ironstone bands, differential erosion creates terraced slopes and benches rather than individual pillars.
The fossil record
The Cretaceous sediments of the Drumheller area and the adjacent Dinosaur Provincial Park (located near Brooks, Alberta) preserve one of the world's most complete records of Late Cretaceous terrestrial and nearshore life. The rock units exposed here were deposited on the well-watered coastal plains adjacent to the Western Interior Seaway — an environment that supported large populations of dinosaurs, crocodilians, turtles, fish, and early mammals.
Dinosaur Provincial Park, designated a UNESCO World Heritage Site in 1979, has produced more than 40 dinosaur species and tens of thousands of specimens. The park is managed by Alberta Parks and the Royal Tyrrell Museum of Palaeontology, which is located in Drumheller and operates as one of the leading palaeontological research institutions in North America.
Palaeontological fieldwork in the Alberta badlands has been continuous since the late 19th century. The Barnum Brown expeditions for the American Museum of Natural History (1910–1915) removed hundreds of complete skeletons. Subsequent work by the National Museum of Canada and later the Royal Tyrrell Museum documented the stratigraphy in detail, enabling species to be correlated with specific geological horizons and, by extension, specific time periods within the Cretaceous.
Stratigraphy and coal
The dark bands visible in many badland exposures are coal seams — remnants of ancient swamp and floodplain forest. The Drumheller coal seams were commercially mined from the 1910s through to the 1950s and early 1960s, driving the growth of the town. At peak production in the 1940s, the Drumheller coalfield employed several thousand miners and supplied fuel to western Canada's railways and heating market. The seams are typically 1 to 2 metres thick and composed of sub-bituminous coal.
The alternating light and dark banding in the valley walls — pale grey mudstone, cream-coloured sandstone, and black coal — is one of the most distinctive visual features of the landscape and records the repeated alternation between swampy forested environments and river or floodplain conditions over roughly 10 million years of Cretaceous time.
A group of hoodoos in Drumheller. The flat-topped caps are boulders or concretions of harder ironstone; the columns beneath are softer mudstone. Photo: G. Larson / Wikimedia Commons / Public domain.
Niagara Escarpment: a comparison
The Alberta badlands and the Niagara Escarpment represent two ends of the Canadian sedimentary geology spectrum. The Escarpment — a 725-kilometre-long dolomite ridge running from Niagara Falls north and west through Ontario — is resistant rock exposed by differential erosion of the softer shales beneath it. The badlands are the opposite: the soft rock is what's exposed, and the resistant elements (the capstones) are what remain as remnants.
Both, however, are products of the same fundamental process: water eroding differentially through rock layers of varying hardness. The Niagara Escarpment produces cliffs; the Alberta badlands produce hoodoos and coulees. The difference is in the geometry of the rock layers and the direction of erosion.
Further reading
The Royal Tyrrell Museum of Palaeontology publishes field guides and research papers through its institutional repository. tyrrellmuseum.com is the starting point for current research. For the regional stratigraphy, the Alberta Energy Regulator and the Alberta Geological Survey maintain open-access geological maps and formation summaries at ags.aer.ca.