Fort Peck Reservoir is an outdoorsman's paradise, with incredible fishing opportunities. Some of the best big game hunting in the state can be found in the surrounding region and for those searching for solitude, it can be easy to find in the Fort Peck area. It's also a paradise for geology nerds.

Credit: US Army Corp of Engineers - Omaha District
Bowling Ball Ridge, Fort Peck. Credit: US Army Corp of Engineers - Omaha District
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Perfectly round rocks can commonly be found.

Most rocks in nature aren't perfectly round. Erosion, fracturing, volcanic forces, pressure plates, etc., usually form rocks in not-round shapes. However, in much of Eastern Montana, it's not unusual to find spherical rocks. Tourists or the uninformed may think the round rocks are fossilized dinosaur eggs, but they're certainly not.

Credit: US Army Corp of Engineers - Omaha District
Credit: US Army Corp of Engineers - Omaha District
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The round rocks are called concretions.

Fort Peck Reservoir was built by the US Army Corp of Engineers (constructed from1933 - 1940) and they maintain the massive body of water. They recently shared a really interesting post describing "Bowling Ball Ridge" and how the round balls of hardened sediment were formed during the Cretaceous Period. At one time, most of Montana (as well as Wyoming, Colorado, the Dakotas, New Mexico, and Texas) were covered in a relatively shallow ancient seabed, called the Western Interior Seaway.

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Credit: US Army Corp of Engineers - Omaha District
Credit: US Army Corp of Engineers - Omaha District
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The round rock concretions come in all sizes.

The prehistoric seabed that covered a large portion of the western US helped create the interesting round rock balls (as well as tons of fossils and oil). Some are nearly perfectly round, others are egg-shaped and they can be found in various sizes, from marble/golf ball dimensions all the way up to the size of a small car. On "Bowling Ball Ridge" a series of large, round, rock balls line up nearly perfectly as the hill slopes down to the lake.

Western Montana gets a lot of attention for its mountains and beauty, but don't ignore the wide-open grandeur of Eastern Montana. With fossils, fishing, and true "Big Skies" a trip to the Fort Peck area is well worth exploring.

LOOK: Stunning vintage photos capture the beauty of America's national parks

Today these parks are located throughout the country in 25 states and the U.S. Virgin Islands. The land encompassing them was either purchased or donated, though much of it had been inhabited by native people for thousands of years before the founding of the United States. These areas are protected and revered as educational resources about the natural world, and as spaces for exploration.

Keep scrolling for 50 vintage photos that show the beauty of America's national parks.