Uncovering Time: The Hell Creek Basin
A prime window into the Earth’s past — home to the final champions of the dinosaurs and the backdrop to one of the planet's most pivotal extinction events.
What Is the Hell Creek Formation?
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The Hell Creek Formation dates from the Late Cretaceous, around 66 million years ago.
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It extends across Montana, North Dakota, South Dakota, and Wyoming, with equivalent formations in eastern Wyoming known as the Lance Formation.
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Renowned for preserving fossils from the end of the dinosaur era, including iconic species like T. rex and Triceratops.
Did You Know?
The formation gets its name from Hell Creek in Jordan, Montana, but it spans far beyond—including beneath Hell Creek Ranch & Cattle
Sources: Hell Creek Formation. Encyclopedia Britannica. https://www.britannica.com/science/Hell-Creek-Formation, Hell Creek Formation. Wikipedia. https://en.wikipedia.org/wiki/Hell_Creek_Formation, The Amazing Hell Creek Formation. Everything Dinosaur Blog, 2025. https://blog.everythingdinosaur.com/blog/_archives/2025/02/23/the-amazing-hell-creek-formation.html, North Dakota Geological Survey – Paleontology Notes. ND Department of Mineral Resources. https://www.dmr.nd.gov/ndgs/ndnotes/ndn12.htm
Dinosaurs & Creatures of Hell Creek
Fossil | Description / Fun Fact | |
|---|---|---|
Tyrannosaurus rex | Apex predator. ~24% of large dino fossils. Fun Fact: 'Sue' and 'Stan' were found in this formation.
Source: https://en.wikipedia.org/wiki/Hell_Creek_Formation | |
Triceratops | Most common herbivore. Shows horn battle damage. Fun Fact: May account for 40% of all Hell Creek fossils.
Source: https://dino-world.com/inside-the-hell-creek-formation-what-the-last-days-of-the-dinosaurs-looked-like-1-12143/ | |
Edmontosaurus | Duck-billed hadrosaur. Often found in groups.
Source: https://en.wikipedia.org/wiki/Edmontosaurus | |
Ankylosaurus | Armored plant-eater with a tail club. Rare in Hell Creek.
Source: https://en.wikipedia.org/wiki/Ankylosaurus | |
Pachycephalosaurus | Thick-skulled dinosaur—possibly used headbutting for mating rights.
Source: https://www.mdt.mt.gov/travinfo/docs/roadsigns/HellCreek1.pdf | |
Other Vertebrates | Includes fossil turtles, crocs, fish, amphibians, and early mammals.
Source: https://en.wikipedia.org/wiki/Paleobiota_of_the_Hell_Creek_Formation |
A Changing World – “Life Before & After the Asteroid”
What is now the rolling grasslands and rocky outcrops of Hell Creek Ranch & Cattle was once a vibrant, subtropical floodplain teeming with prehistoric life.
During the Late Cretaceous Period, this landscape was covered in dense conifer forests, ferns, flowering plants, and braided river systems. Herds of Triceratops, Edmontosaurus, and armored Ankylosaurs roamed the land, while predators like Tyrannosaurus rex ruled the food chain. Fish, turtles, crocodiles, and early mammals lived in the surrounding wetlands, forming a diverse and dynamic ecosystem.
But around 66 million years ago, the world changed forever.
A massive asteroid impact off the coast of what is now Mexico triggered the Cretaceous–Paleogene (K–Pg) extinction event, wiping out nearly 75% of all species—including the non-avian dinosaurs. Layers of ash and sediment buried the land, preserving the moment of extinction within the very rock beneath our feet.
Today, those same hills tell a silent story—etched into stone, fossil by fossil.
“The Hell Creek Formation is one of the only places on Earth where you can trace life before and after the extinction. It’s not just land—it’s a fossilized moment in deep time.”
— Dr. James Fassett, Paleogeologist
The Geology Beneath Our Boots
Sources: Hell Creek Formation. Encyclopedia Britannica. https://www.britannica.com/science/Hell-Creek-Formation, Hell Creek Formation. Wikipedia. https://en.wikipedia.org/wiki/Hell_Creek_Formation, The Amazing Hell Creek Formation. Everything Dinosaur Blog, 2025. https://blog.everythingdinosaur.com/blog/_archives/2025/02/23/the-amazing-hell-creek-formation.html, North Dakota Geological Survey – Paleontology Notes. ND Department of Mineral Resources. https://www.dmr.nd.gov/ndgs/ndnotes/ndn12.htm, The Day the Dinosaurs Died. The New Yorker. https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died, Stratigraphy of the Hell Creek Formation and the Cretaceous–Paleogene Boundary. ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0195667115300306 Paleobiota of the Hell Creek Formation. Wikipedia. https://en.wikipedia.org/wiki/Paleobiota_of_the_Hell_Creek_Formation, Tanis Fossil Site. Wikipedia. https://en.wikipedia.org/wiki/Tanis_(fossil_site)
Did You Know?
Fossils found here aren’t just bones—they include plant material, fish, insects, and even fossilized turtle shells and crocodile teeth. Every one of them was buried and preserved by the very earth you’re standing on.
At first glance, Hell Creek Ranch & Cattle may seem like a quiet expanse of rolling hills and dry grass—but just beneath the surface lies one of the most scientifically significant rock formations in the world.
This land is part of the Hell Creek Formation, a stacked record of ancient river channels, floodplains, and swamps laid down over 2 million years during the Late Cretaceous period, around 66 million years ago.
The ground under your boots is made up of sandstone, siltstone, shale, mudstone, and lignite—layer upon layer of Earth’s memory. These sediments were deposited by ancient rivers that once flowed through subtropical forests, gradually building the fossil-rich rock beds we see today.
Over time, erosion from wind, rain, and freeze-thaw cycles carved the badlands and exposed fossils like pages in a stone-bound book. This natural process continues today, revealing new discoveries each season—sometimes even by chance, right here on the ranch.
The distinct layering of the Hell Creek Formation also includes a thin but world-famous band of clay enriched with iridium—a rare metal linked to the asteroid that triggered the mass extinction of the dinosaurs. This K–Pg boundary layer serves as a literal line in the rock, separating two worlds: one full of dinosaurs, and one without.
Sources: Hell Creek Formation. Encyclopedia Britannica. https://www.britannica.com/science/Hell-Creek-Formation, Hell Creek Formation. Wikipedia. https://en.wikipedia.org/wiki/Hell_Creek_Formation, The Amazing Hell Creek Formation. Everything Dinosaur Blog, 2025. https://blog.everythingdinosaur.com/blog/_archives/2025/02/23/the-amazing-hell-creek-formation.html, North Dakota Geological Survey – Paleontology Notes. ND Department of Mineral Resources. https://www.dmr.nd.gov/ndgs/ndnotes/ndn12.htm, Stratigraphy and Depositional Environments of the Hell Creek Formation. Rocky Mountain Geology / GeoScienceWorld. https://pubs.geoscienceworld.org/uwyo/rmg/article-abstract/39/2/93/87979 Inside the Hell Creek Formation: What the Last Days of the Dinosaurs Looked Like. Dino-World.com. https://dino-world.com/inside-the-hell-creek-formation-what-the-last-days-of-the-dinosaurs-looked-like-1-12143, Prehistoric Life in North Dakota – Hell Creek Map. ND Geological Survey. https://www.dmr.nd.gov/dmr/sites/www/files/documents/paleontology/pdfs/prehistoric-life-map/Hell_Creek.pdf, Paleobiota of the Hell Creek Formation. Wikipedia. https://en.wikipedia.org/wiki/Paleobiota_of_the_Hell_Creek_Formation