St. Mary River Formation, Geological formation in Alberta, Canada and Montana, United States.
The St. Mary River Formation is a geological sequence spanning southwestern Alberta and northwestern Montana, composed of sandstone, mudstone, and coal layers. This rock sequence reaches thicknesses exceeding 700 meters in some areas and displays the varied sediments that accumulated over long periods.
The formation developed during the Late Cretaceous period roughly 72 to 67 million years ago, when the region was covered by water or shaped by river environments. George Mercer Dawson first documented these layers scientifically in the 1880s and established the geological name.
The layers contain fossils of plants and sea creatures that visitors can observe in the rock formations today. These remains provide a direct view into what inhabited the region during ancient times.
The area is accessible at various locations across Alberta and Montana where the layers are exposed at ground level. Visitors should wear sturdy footwear and be prepared for uneven terrain, especially when searching for fossils or traces.
The formation preserves more than 100 track-bearing layers from different dinosaur species, showing that plant-eating and meat-eating types roamed the region. These footprints remain visible today and offer rare insights into the behavior and movement patterns of these ancient animals.
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