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Not all who wander are lost. Some are looking for rocks.

Nowhere is this more true than in Montana. Musselshell County and Eastern Montana are truly a rock hounders dream come true. Few other areas have such a diverse mix of geology from a wide range of formations and eras. With different formations and rocks in all four directions, Roundup is the perfect home base for your family's next rock adventure.

If you can divert your eyes from the beauty of Big Sky Country, you are sure to find unique treasures sitting just beneath your feet. From world famous gemstones like Yogo Saphires and Montana Agates to prehistoric fossils from the land and sea, Roundup Montana should surely be on every rock enthusiast’s bucket list. These are some of my family’s favorite locations.

Western Interior Seaway Fossils Much of Eastern Montana and the Central United States were covered by an interior seaway and coastal plains during the mid to late cretaceous period. Areas around Melstone, Winnett and Mosby offer opportunities to explore several geologic formations from this time period. Aquatic fossils that can be found in abundance include: Ammonites & Baculites, shark teeth, clam & oyster shells, and the remains of marine reptiles like Mosasaurs and Plesiosaurs. Adjacent formations also include land animals like our official state dinosaur, the Hadrosaur, as well as some of the last dinosaurs to roam our earth.

(Important note: Vertebrate fossils may only be collected on private property with landowner permission. They may not be collected on public land. Invertebrate fossils such as shells, ammonites, and baculites may be collected on public land.)

Yellowstone River Agates Montana is world famous for its agates! Treasure State Agates, Montana Moss Agates, and Dryhead Agates are commonly found in and along the Yellowstone River and its tributaries. Hundreds of miles of the Yellowstone River are accessible with only an hour or two of driving from Roundup. From Columbus to Glendive, there are many areas of public access to the river and surrounding areas. Simply walk the gravel bars and see what treasures the river has uncovered!

Snowy Mountain Fossils Looming to the northwest of Roundup, the Snowy Mountains offer beautiful scenery, wildlife, and fossils. Formations ranging between the Paleozoic and Mesozoic eras offer many opportunities for finding aquatic fossils. Brachiopods, Corals, and Crinoids can be found embedded in limestone formations throughout the mountains. Several of our favorite targets are the beautiful Linoproductus shells found among the limestone seams and unique star shaped crinoid sections.

Judith Mountain Quartz Crystals a scenic drive 70 miles North of Roundup can find you atop the 5800’ Judith Peak in the Judith Mountains. The road to the peak offers opportunities to scour the hillsides for “Montana Diamonds”. These double terminated quartz crystals are of slightly lesser quality than the famous “Herkimer Diamonds” found in New York State. They are easily found by screening the dirt or simply picking them from the surface.

Sandstone Fossils The sandy hills directly surrounding the town of Roundup are teeming with fossils as well. The Fort Union Formation makes up much of the sandstone and coal bearing areas around Roundup. This Paleocene era formation was built up during a time of swamps and wetlands. Exploring the rocky outcroppings of layered sandstone can produce embedded fossils of leaves, plants, fish, and mammals. These fossils are often quite fragile and will degrade when exposed to open air unless they are preserved shortly after discovery.

Build your own rockhound kit and head for the hills. Your next favorite rock is waiting for you just outside of Roundup, MT.


Eric Eliasson is a long-time resident of Roundup, MT, A master electrician, and an avid rock and fossil hunter. Along with his wife, Kendall, and son, Dylan, they explore Montana looking for unique rocks and experiences. Together Eric and Kendall also make and sell stone jewelry that celebrates the unique geology that surrounds Roundup. Learn more about them and their rock hounding adventures at

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