If you want to read the final, violent chapters of the Mesozoic Era, you do not go to the jungle or the coast. You go to the dry, eroded badlands of Montana. Here, the earth has been stripped of its topsoil and carved by wind and water into a maze of coulees and hoodoos. What remains exposed at the surface is a staggering concentration of fossilized bone, an archive of deep time that has fundamentally changed our understanding of life on Earth.
Montana is North America's legendary boneyard. The sheer volume of fossils found here is not an accident of biology, but a consequence of geology. Between 100 and 66 million years ago, a vast inland ocean known as the Western Interior Seaway split the continent. As this sea advanced and retreated, massive river systems carried sand and mud from the rising Rocky Mountains to the west, depositing thick layers of sediment across a broad, low-lying coastal plain. When the dinosaurs died, they were rapidly buried in this sediment, sealed away from scavengers and decay. Millions of years later, the arid climate of eastern and central Montana eroded those sediments, bringing the deep past back to the surface.
To understand the paleontology of Montana is to understand two massive geologic formations: the Two Medicine and the Hell Creek.
The Two Medicine Formation and the Caring Mother
In the northwestern part of the state, near the town of Choteau, the Two Medicine Formation outcrops in a landscape of shortgrass prairie and rolling hills. The sediments here were deposited during the Campanian stage of the Late Cretaceous, roughly 77 to 74 million years ago. At the time, this was an upper coastal plain, a semiarid environment punctuated by the ash falls of nearby erupting volcanoes.
It was here, in 1977, that Marion Brandvold, the owner of a local rock shop in Bynum, made a discovery that would alter the course of paleontology. She found the tiny, fossilized remains of juvenile dinosaurs. The following year, she showed the site to paleontologist Jack Horner. Horner and his team began excavating the area they would name Egg Mountain. They uncovered not just isolated bones, but fourteen distinct dinosaur nests in a single area.
The nests belonged to a previously unknown species of hadrosaur, a duck-billed dinosaur that Horner named Maiasaura peeblesorum, which translates to "caring mother lizard." The discovery provided the first concrete evidence that dinosaurs were not simply giant, cold-blooded reptiles that abandoned their eggs, but complex, social animals that fed and cared for their young. The evidence from Egg Mountain showed that Maiasaura nested in vast colonies, returning to the same grounds year after year, and nurturing their hatchlings until they were large enough to join the herd. Today, Maiasaura is the official state fossil of Montana. The story is preserved at the Old Trail Museum in Choteau and the Montana Dinosaur Center in Bynum.
The Hell Creek Formation and the End of an Era
Move east across the state, toward the Dakotas, and you enter the domain of the Hell Creek Formation. This geologic unit was deposited during the Maastrichtian stage, the very end of the Late Cretaceous, approximately 66 million years ago. It represents the last gasp of the dinosaurs before the asteroid impact that ended their reign.
The Hell Creek is a layer of sandstone, mudstone, and clay that spans nearly 700 kilometers across the region, reaching thicknesses of up to 170 meters. It was deposited by large, meandering rivers flowing across a humid, subtropical coastal plain. The environment was lush, teeming with flowering plants, early mammals, and the undisputed apex predators of the Late Cretaceous.
It was in the Hell Creek rocks near Jordan, Montana, in 1902, that professional fossil hunter Barnum Brown made a monumental discovery. Working for the American Museum of Natural History, Brown unearthed the world's first identified skeleton of Tyrannosaurus rex. Nearly a century later, in 1988, Kathy Wankel discovered another T. rex near Fort Peck Lake. The Wankel T. rex is now the centerpiece of the Smithsonian's National Museum of Natural History, mounted in a pose devouring a Triceratops. Visit the Garfield County Museum and the Fort Peck Interpretive Center to see this chapter of the trail.
The Hell Creek Formation is the premier window into the world immediately preceding the K-Pg extinction event. The rocks here hold the bones of Triceratops, the armored Ankylosaurus, the dome-headed Pachycephalosaurus, and the massive Edmontosaurus. Interspersed among the bones are layers of volcanic ash, which allow geologists to radiometrically date the fossils with extraordinary precision. In the badlands of Makoshika State Park near Glendive, those sediments are open to the sky.
The Dinosaur Trail
The paleontology of Montana is not confined to academic papers and distant museums. The state has embraced its deep history, organizing a network of museums and field stations known as the Montana Dinosaur Trail.
From the world's best-preserved dinosaur mummy, a Brachylophosaurus named "Leonardo" in Malta, to the massive collection of T. rex skulls at the Museum of the Rockies in Bozeman, the trail offers a tangible connection to the Mesozoic. Several facilities along the trail even offer public field digs, allowing anyone to take a trowel to the dirt and search for the bones of the Cretaceous.
The articles linked below explore the specific locations where this history is preserved and displayed. They trace a path across the badlands and the prairie, following the rivers of sediment that captured a lost world.
- Museum of the Rockies (Bozeman)
- The Montana Dinosaur Center (Bynum)
- Old Trail Museum (Choteau)
- Great Plains Dinosaur Museum (Malta)
- Phillips County Museum (Malta)
- Fort Peck Interpretive Center (Fort Peck)
- Garfield County Museum (Jordan)
- Carter County Museum (Ekalaka)
- Makoshika State Park (Glendive)
- Frontier Gateway Museum (Glendive)
- H. Earl Clack Memorial Museum (Havre)
- Depot Museum (Rudyard)
- Blaine County Museum (Chinook)
- Upper Musselshell Museum (Harlowton)
- Musselshell Valley Historical Museum (Roundup)