Writing-On-Stone Provincial Park
Milk River Formation
Sweetgrass Hills
Native People
Northwest Mounted Police
Early Settlement
About the River

The Milk River Formation


Late Cretaceous Inland Sea
Geological Time Scale
The Milk River Formation
Deadhorse Coulee Member
Late Cretaceous Inland Sea
About 85 million years ago, a huge inland sea covered the middle of North America. The location of Writing-On-Stone, on the Milk River, would have been located on this very large and stormy sea. Sand was deposited on the shore which, over millions and millions of years, slowly compacted to become sandstone rock. This became part of the Milk River Formation.

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Geological Time Scale

Era Period Formations Events
65 million years ago 
to present
Quaternary 10-15 thousand year ago: last Ice Age ends
1 million years ago: North American Ice Ages begin
Tertiary Cypress Hills
Porcupine Hills
Willow Creek
48 million years ago: formation of Sweet Grass Hills
225 million year ago
to 65 million years ago
Cretaceous Whitemud
St. Mary River
Blood Reserve
Milk River
Rocky Mountains uplifting

65 million years ago: last dinosaurs

225 million years ago: first dinosaurs
570 million years ago
to 225 million years ago
Prior to 
570 million years ago
Formation of Earth's Crust 4,600 million years ago.

This is a synthesis of information from many different sources.
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The Milk River Formation
Over millions and millions of years, the beach on the Late Cretaceous Inland Sea became buried. The weight of the material covering this sand compacted it into hard sandstone rock. This sandstone is evident where the Milk River Formation is exposed.

The Milk River Formation has three main components:

  • Deadhorse Coulee Member
  • Virgelle Member (Upper and Lower)
  • Telegraph Creek Member
  • The Virgelle Member of the Milk River Formation consists of magnificent sandstone cliffs. Upper Virgelle, being softer, is characterized by the presence of impressive hoodoos, as seen at the top of this picture. Lower Virgelle, bottom of the cliffs, is characterized by relatively dense (hard) on which there is native rock art.

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    Deadhorse Coulee Member
    One characteristic of the Deadhorse Coulee member is the presence of conspicuous mounds and badland landscapes. Both of these formations have a high bentonite clay content. Click on the two pictures below for a closer look.
    Bentonite clay is a swelling-and-shrinking clay. When wet, the clay expands and is extremely slippery. When it dries, the clay shrinks back to its original size and can assume a popcorn-like structure. Often found on the surface of bentonite clays are gypsum crystals (CaSO4-H20), seen here just above camera lens. These crystals form as a result of repeated wet and dry periods.

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    North America During the Last 150,000 Years
    Terrain Sciences Division of Natural Resources Canada
    Alberta Geography
    Canadian Landforms (Cyberwall)