The Missouri River from the Pleistocene to the Present
By Elena Ulev
It’s time for Field Notes, brought to you by the Montana Natural History Center.
Black Angus cows. I squint my eyes and imagine that they’re bison. A dilapidated root cellar. I squint again and imagine it’s a tipi. Other than those two modern-day sights, I could be canoeing through this riverine landscape, now the Upper Missouri Breaks National Monument, hundreds of years ago. One might wonder how much this landscape has changed, and the answer is: it has changed dramatically. This amazing place has seen it all, from a giant sea to volcanoes and glaciers to today’s semi-arid desert.
Around 90 million years ago, a shallow inland sea stretched from the Arctic through the west central United States and south to the Gulf of Mexico, splitting the continent into two landmasses. Dinosaurs like apatosauruses roamed the area and pterodactyls flew overhead. Then the sea shrank and tectonic plates converged and diverged, which, together with volcanic activity, formed Montana’s mountain ranges. This was approximately 50 million years ago. Then, around 15,000 years ago, our last ice age occurred, and glaciers reversed the Missouri River from a northward flow into the Hudson Bay to a permanent southward flow into the Gulf of Mexico.
Today’s landscape looks much the same as it did 500 years ago. The ancient sea, with its expanding and contracting shorelines, deposited millions of tons of sand, silt, and clay, and they lithified into sandstone, forming dramatic and strange formations. The Eagle Sandstone cliffs are still here, as are the igneous dikes, protruding upward like gigantic black shark fins amongst the cliffs. The rolling hills of sagebrush, yucca, and rubber rabbitbrush still dominate the landscape as far as the horizon.
Canoeing this 46-mile stretch for the second time is even better than the first—I know what to expect and I notice more. I see smooth white cliffs with dozens of Cliff Swallows’ mud nests tucked into the eaves like little gray beehives. Three White Pelicans fly overhead, change direction, and come back again as a Bald Eagle screeches from a gigantic plains cottonwood tree on the river’s edge. I wonder how much the towering cliffs have eroded since Indigenous people occupied this area. Have they eroded two feet? Fifty feet? I paddle past a weird sandstone formation that looks like a group of twenty-foot tall people discussing something important. They have faces, hats, and even clothes. Water that resembles chocolate milk, murky with bentonite clay from ancient volcanic ash, carries my canoe along at a steady three miles per hour. Despite the opaque water, I take an evening swim in the wide river anyway, feeling the fine grit in my teeth every time I raise my head from the water.
The Upper Missouri Breaks are devoid of human-made sounds—there are no vehicles, no motorboats, not even airplanes flying overhead. I hear a handful of animals: a Rock Wren trilling, buzzing bees pollinating an aster, and the splash of a fish jumping. At dusk I listen to a group of coyotes howl. I imagine them standing together, heads pulled back, singing their yippy yappy songs. Are they anticipating the evening’s hunt to come? Are they mourning? Listening to them makes me feel happy and lonesome at the same time.
I pull a yellow flower from a mustard plant and enjoy its horseradish flavor as I chew and watch the sunset. I wonder what this landscape will look like 500 years from now. This gem of a place has experienced so many huge geological phenomena that I imagine was once ear-piercing, from dinosaurs fighting to giant beavers gnawing down giant trees, volcanoes erupting, and glaciers groaning southward—but it is quiet now. A lovely and very rare kind of quiet.
This is Elena Ulev for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. For more information on upcoming programs and events at the Center, call 406.327.0405 or visit our website at MontanaNaturalist.org.
