by Daniel B. Botkin, originally published by Perigee Books, a division of Penguin/Putnam, 1999.

This book, originally published as “Passage of Discovery“, is an ecologist’s guide to the first half of the Lewis and Clark trail, their travels up the Missouri River from St. Louis to Three Forks, MT.  I have decided to share this book with the readers of my website, and I am going to present the entire book here, one chapter at a time, with a new chapter appearing each week.  There are more than 40 chapters.  If you follow along and read all of them, you will learn about the entire Missouri River as seen by Lewis and Clark at the beginning of the 19th century, and as I visited it during the 1990s to see what they had seen, and to learn how the countryside had changed.  Comparing what Lewis and Clark saw with what we see today is one of the best insights we can get of how nature and environment in American has changed since European settlement.   I hope you enjoy it and find it rewarding.

- Daniel B. Botkin

All of the chapters published thus far can be found in the Passage of Discovery category. Please note that they are listed in reverse order of date posted.

More books by Daniel Botkin are available for purchase from the Center For the Study Of the Environment bookstore.

34. Fort Peck Dam and the Milk River: How the Ice Ages Altered the Course of the Missouri River

To Fort Peck Dam: From the north take U.S. Route 2 to Nashua, then Route 117 south to Route 24, which goes along the reservoir, Fort Peck Lake.  Turn left to the dam.  From the south take Route 200 to Route 24; take Route 24 north to the dam.

To see the Milk River: Take Route 2 west from Nashua.  The route passes now and again near the river.  Route 24 northwest from Fort Peck Dam goes to Glasgow where it passes a park along the Milk River in that town.

The Hewitt Lake and Bowdon National Wildlife Refuges are near Malta, Montana and are reached by following Route 2 west from Fort Peck. Bowdon National Wildlife Refuge is off Route 2 one mile east of Malta.  There turn east onto Old Highway 2.  The refuge headquarters is six miles down this road.  To reach Hewitt Lake National Wildlife Refuge,  from Malta take Route 2 east, then take a side road north toward Cree Crossing.  Then take a gravel road west across Nelson Reservoir.  The refuge is two miles west. It is advised that you use USGS or BLM local maps for details to reach this refuge.

A curious change occurs on the Missouri River upstream from Fort Peck Dam and from there to Loma, near Fort Benton, Montana.  The river you can see at Fort Benton or on a float trip through the white cliffs, wild and scenic portion of the Missouri River is very different from the river as it flows upstream from Great Falls or downstream from Fort Peck Dam.

Lewis and Clark saw this change in the Missouri River as they slowly moved upstream in the spring of 1805.  On May 7, 1805, the expedition was just downstream from the location of modern Fort Peck Dam, where Lewis wrote that “the country we passed today on the North side of the river is one of the most beautifull plains we have yet seen.”  He saw that the land rose “gradually” away from the river “to the hight of 50 or 60 feet, then becoming level as a bowling green.” That green landscape extended “as back as far as the eye can reach.”   But the floodplain of the Missouri changed abruptly upstream.  Four days later, on May 11, 1805, when the expedition was a little way upstream from the present site of that dam, Clark wrote that the “high land is rugged and approaches nearer than below, the hills and bluffs exhibit more mineral . . .  Salts than below.”   Lewis’s journal confirms this change with almost identical wording.  Below the site of Fort Peck, the Missouri flowed then, as it does today, in a wide and gently sloping valley.  Above the site of that dam, the river flowed through a narrow and steep valley.  Today, this change is not visible in a single view, because the upstream portion at Fort Peck Dam is covered by water.  But you can see the change when you compare the Missouri River that you see from the causeway below Fort Peck Dam with the Missouri you can see when you visit Fort Benton, Loma, Judith Landing, or Virgelle, Montana, and especially if you are able to take a boat trip down the famous white cliff section of the river.

I wondered why the river was so different in these two sections.  I thought perhaps it was simply because the upper Missouri section was relatively near to the headwaters and the Rocky Mountains, where the river still carried a heavy load of sediment that could knife a steep edge into the countryside.  But the Missouri upstream from Great Falls flows in a wider valley, not so steep as in the white cliffs section, so this explanation couldn’t be right.

A key to the reason that the upper Missouri River is so different from the lower is in a visit to the Milk River, a tributary that flows into the Missouri just below Fort Peck Dam.  That river has a different look and a different setting than the Missouri upstream from the dam.

Lewis saw the difference when he walked upstream on the Milk River. The expedition arrived at the mouth of the Milk River on May 8, 1805.  “We nooned it just above the entrance of a large river,” he wrote, and continued that he “took the advantage of this leasure moment and examined the river for about 3 miles.”  He found the Milk River to be deep and gentle with a “large boddy of water,” But most important he saw that “the bottoms of this stream are wide, level, fertile.”  He named it the “Milk River” because the water had “a peculiar whiteness, being about the colour of a cup of tea with the admixture of a tablespoonfull of milk.”

Lewis and Clark observed each of the rivers they came across carefully.  They wrote down each river’s characteristics, and gave the rivers names.  Theirs was a careful, natural history examination.  This is not the way most of us view rivers in the countryside.  Most of the time when we travel we accept the countryside as it is, as a static picture passing by us, without questioning how it came about.  But rivers on a landscape are telling us a story – a story about their history, why they are the kind of river we see.  Now here was a curiosity: two rivers coming together on the same landscape at the same location, but one, the Missouri, had cut itself steeply between bluffs while the other, the Milk River, flowed in a wide and gentle floodplain.  What caused the difference?

Geologists talk about “uniformitarianism,” a big word that means that the processes that exist today existed in the past, and also that the processes that occur in one place occur in another — the physical, chemical and biological processes that create a landscape have to follow the same rules of nature everywhere, in time and in space.  If that is true, then the Milk and Missouri River ought to look the same and flow in similar valleys.  Then how can these two rivers be so different?

It’s a curious question, and the answer lies in effects of the great continental ice sheets on the Missouri River tens of thousands of years ago.  During the last ice age, the ice sheet pushed down from Canada all the way to the Missouri River in this part of Montana. The ice was an irresistible force, and the Missouri, that mighty river, was not quite the immovable object.  The ice pushed the river out of its old bed along a section between Loma and Fort Peck.  The ice began to melt back about 15,000 years ago.

When we see a great river, it appears to us as a permanent and unchanging part of the landscape.  But a river has a history and goes through stages from young to mature.  When a river first starts to flow on a landscape, it cuts straight down.  The sediment that it carries wears away at the land.  A young river flows in a narrow valley with steep sides.  But over a much longer time, the river keeps undercutting the bluffs along its narrow valley. The bluffs collapse.  Lewis and Clark saw cliffs that had fallen into the Missouri just this way.  The river then moves the debris from those fallen bluffs downstream.  Slowly the valley widens.  The slopes become gentle.  When the valley is wide enough, the river can meander over it, and over the years it shifts its channel, creating oxbows, oxbow lakes, backwaters.  It becomes a mature river in a mature river valley.

The Missouri is an ancient river and for most of its length it flows through the wide and gently sloping valley that characterizes such a river.  But when the ice sheet pushed the Missouri out of its old bed, the river was forced to create a new one.  During the height of the ice age, the Missouri was pushed south and forced to flow just to the south of the ice where it began to cut a new valley into the countryside.  Once that valley was formed, the river was captured by it.  When the ice sheet retreated, it left debris in the Missouri’s old channel.  The river had cut its way down into the new one  and continues to flow through it today, from Loma to Fort Peck.  From Great Falls to Loma, the Missouri flows through a wide valley. But because of glaciers long ago, at Loma the Missouri begins to flow through a narrow canyon and continues to do so past where Lewis and Clark noticed the change in the countryside.

As the ice sheet melted, it left debris of boulders, rocks, sand, silt, and clay everywhere, helter-skelter, mixed together, but also somewhat smoothed out.  The beautiful plain that Lewis saw where the Milk River flows into the Missouri, at the site of present-day Fort Peck, was bull-dozed by the glaciers to create the rolling but relatively flat and pretty countryside that Lewis found so beautiful.  Huge boulders, here and there, dropped by the glaciers, are markers and testimony to the powerful work done by the moving sheets of ice.  They stand along the roadside to remind us of that awe-ful geologic history.

After the ice sheet retreated the Milk River began to flow in part of the Missouri’s  old channel.  A smaller river, it passes through a plain too big for it to have created.  It is a young river in an old river’s arms.

From Fort Peck Dam, you can travel to see the Milk River by going up to Nashua, Glasgow, or Malta, visiting the Hewitt Lake National Wildlife Refuge, which is on the big bend of the Milk River, or the Bowdon National Wildlife Refuge.  When you do this, you are seeing the original valley of the Missouri.  Just imagine a bigger river in this valley and you will be able to imagine the way that this countryside would look today if there had never been the great climate change of the ice age, a time when ice hundreds of feet thick pushed aside the landscape in its path, scraped and eroded mountains and hills, dumped the rocks and soil it had cut into valleys, disrupting the rivers, covering the forests.  As I traveled along the upper Missouri, I thought about the great irony of this history – an incredible large-scale change in the land — the arrival of a huge sheet of ice that persisted for thousands of years.  An environmental change that we would not want to happen now that we are occupying the land, and would do whatever we could to prevent the migration of  the Missouri River into a new channel that is now considered its most beautiful stretch.