Nature
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About 65 million years ago, as the Western Interior Seaway receded and the Rocky Mountains rose, great rivers meandered through a warm, humid coastal plain and deposited the sediments that later became the Hell Creek Formation. Its tan sandstones, siltstones, and mudstones are common across eastern Montana and are especially visible in highway road cuts, the Charles M. Russell Wildlife Refuge, and Makoshika State Park. Dinosaur fossils are frequently found there, including Triceratops, Edmontosaurus, Pachycephaosaurus, Ankylosaurus, and Tyrannosaurus rex. The boundary between the late Cretaceous Hell Creek Formation and the more recent Tertiary Fort Union Formation provides evidence that a gigantic meteorite or asteroid struck Earth about 65 million years ago, though it is not known whether that event caused the extinction of the dinosaurs or only hastened it. Fossils excavated and studied in Montana from the Hell Creek Formation have added immeasurably to knowledge of dinosaurs and their lives.
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Montana · United States
