Peabody Fossil Hunter

Saturday, July 9

In Uncategorized on July 9, 2011 at 6:36 am

Today we happened upon a different kind of mammal.

About the size and weight of a Volkswagen Beetle, the American bison is the largest mammal on the continent. The animal we call a buffalo took millennia to evolve from its ancestor that likely crossed the Bering Strait from Asia. It only took 50 years for North Dakota’s first white settlers to drive them to the brink of extinction. Now, a few hundred of the beasts roam the grasslands in Theodore Roosevelt National Park.

An hour’s drive north from Marmarth and a 10-mile hike into the park, we found ourselves face to face with about 30 of the colossal animals. Scattered across a raised plateau of grassland overlooking the Little Missouri River, they looked like giant mounds of brown dirt—until we got too close. With a keen sense of smell, bison become surprisingly nimble the second a person walks within sniffing range. As Matt Raudabaugh approached one particularly large lump, the bull jumped up to its full six-foot height to silently stare us down.

An American bison, or buffalo, weighs as much as a small car.

The bison weren’t the only giants we saw.

On the way into the park, we’d passed through an area known as the Burning Coal Vein, an underground swath of coal that was probably sparked by lightning or a prairie fire. Though it’s dwindled in recent years to a smolder creeping about 10 feet each year, the layer has been burning since the first white settlers came across it almost a century ago, spread out over a corner of the park.

You can’t see the vein from the surface—aside from the rotten egg smell of sulfur, all it emits is hot fumes. But those hot fumes are in the middle of shaping the badlands. Once the coal layer has burned into ash, it leaves weak cavities capable of cracking and caving overlying rock, cutting ravines and exposing a bright pink layer of cooked clay called “scoria.” The park paves its roads out of this brick-like gravel.

Paved in scorched clay, a road cuts through the Burning Coal Vein area of Theodore Roosevelt National Park.

Down the road and a few miles in via dirt trail, we came across another odd phenomenon: giant stone stumps scattered across a valley. The stumps rarely exceed five or six feet in height, but the chunks of petrified wood are all that’s left of an ancient subtropical forest.

About 60 million years ago, around the time when our mammal fossils were still alive, western North Dakota was covered in a dense forest with trees as wide as a standard interstate lane. It’s thought that the conifers, relatives of modern coastal redwoods, became petrified when mountain-building events in the Rockies dumped a coat of volcanic ash over them. Suffocated in an ash cast, the wood was unable to decay naturally. Instead, it absorbed mineralized groundwater that was eventually replaced by quartz crystals. Over time, the brittle splintery stumps eroded out, colored by impurities like iron, carbon, and manganese.

Five feet tall, Natasha Vitek stands next to a petrified tree stump.


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