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3. FORT BENTON TO BIG SANDY, MONTANA
The New Course of the Missouir River
From Fort Benton, we again travel
north on U.S. Highway 87. First head north out of the town on
local road 387 to where it joins Highway 87. Continue to
7.0 miles (11 km) from the west end of the river bridge, or 3.6 miles
(5.7 km) from the junction which enters Highway 87. There is an
unimproved road leading up the hillside to the east, called Rowe Bench
Road on local maps. Continue up the hill as far as the road
will take us; this brings us to the place from where Karl Bodmer in
1832 made several famous paintings of the river with the Bears Paw
Mountains and the Highwood Mountains in the background. There may
be some walking over private land to the overlook [Site 6]. It
would be helpful to refer to the original paintings. Bodmer
altered the perspective to make the mountains appear much closer. The
Bears Paw mountains are barely visible on the horizon of the
photograph; where Bodmer's painting shows the mountains as looming
quite large and rugged.
Bodmer's paintings are showing that the channel of the Missouri River
has changed very little in the past 125 years at this location.
Other, lesser rivers such as the Milk River have shifted significantly
in some places.
Continue on to the town of Loma,
where the Marias River meets the Missouri. To get a good view of
the merging of the rivers, turn off on a local road just south of the
highway bridge over the Marias River. This road takes us to an
overlook (that may not appear on some maps) [Site 7] that is
maintained as a local park. The river in the photograph is the
Marias; the Missouri is just off the frame to the right. The
Marias comes from the Rocky Mountains, originating in Glacier National
Park. It, too, has had its course frequently altered by the
glaciers. Most of the way across the plains the Marias is a
sluggish, muddy river. As it approaches the Missouri it has had
some difficulty cutting down into the land fast enough to keep up
with the much larger river. The Marias River descends quite
steeply over its last few miles—in some places at more than 50
ft/mi (1%). The photograph shows some small rapids caused by
the steep descent in the last mile.
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Lewis and Clark were presented with a dilemma when they came to the Marias River. Their knowledge of the rivers they would encounter on the way to the Rocky Mountains did not account for this river. They expected two principal rivers entering the Missouri from the North, the "White Earth River" and the "River that Scolds All Others." Their counting was probably thrown off by several minor streams shortly after they left their winter camp; one of these they assumed was the White Earth River. To this day one of those small streams in northwestern North Dakota is called the White Earth River or White Earth Creek. These streams all originate nearby on the Missouri Coteau, and not from farther north in Canada, as Lewis and Clark believed. The river known as the White Earth River should have been the Milk River; and was probably known for deposits of fine white kaolin found along its northernmost tributaries. The confusion was aggravated as Lewis and Clark arrived at a time when average precipitation was rather higher than today, and the rivers were flowing full. Somehow most of the party became convinced that the Marias was actually the main river. This seems ridiculous to those who are familiar with the present geography; but the rapids at the mouth could have sugested a powerful river. Moreover, because the Marias is still working hard at cutting a channel through soft rocks, it is full of sediment. Some members of the party thought that the river with more sediment should be the main channel. However when the explorers ascended the Marias for a short distance, it was soon revealed to be a sluggish minor stream over most of its course. The name "River that Scolds All Others" might have arisen because of the rapids near the mouth of the Marias River. |
Highway 87 north of Loma ascends a
steep hill to leave the valley. There are actually two rises.
The first takes one out of the present day Missouri valley; the second takes
us to the rim of the pre-glacial valley. The break in the profile is
subtle, and may be hard to see. From the north end of the bridge,
the first rim is at 1.60 miles (2.57 km), 225 ft (69 m) above the
valley floor; and the second rim is at 3.10 miles (4.99 km), 472 ft
(144 m) above the valley floor. The view toward the south east
from the highest point [Site 8] reveals a much disected land, and a
pre-glacial valley that is over 7 mi (11 km) across.
For those who are equiped with
a four-wheel drive vehicle, there is a magnificent view 18.7 mi (30 km)
northeast from Loma. A short dirt road turns off the main highway
and ascends a small hill to the north. with several radio transmitter
towers. From that point [Site 9] one can see the broad valley in
which lie Big Sandy Creek and the town of Big Sandy. If you notice
it all, you will remark that the creek is far to small to have made
this broad valley. The town is in a relatively narrow part of the
valley, but even there the valley is flat and nearly 3.3 mi (5.3 km)
across. This is the former course of the Missouri River, which
excavated this valley between Big Sandy and the city of Havre. The
ice age glaciers rounded off the sides of the valley to create the
landscape we see today.
The view point is actually on the present-day north-south drainage
divide, which runs along the barely perceptible ridge north of the
highway. North of this point the streams, including Big Sandy
Creek, flow into the Milk River; to the south the streams flow into the
Missouri. The view point is nearly 300 feet (91 m) above the
floor of the valley; which gives an idea of the former relief, and the
depth of the pre-glacial valley.
The ice advancing from the north dammed up the flow of the Missouri
River and created a huge lake, called Lake Great Falls.
When the ice reached as far as the present location of Big Sandy
it must have impounded the lake at a level too low to exit through the
spillway at the Shonkin Sag. At the a water level of 3200 to 3400
feet (975 to 1036 m) the lake could have overflowed a ridge running
from the Bears Paw Mountains to the Judith Mountains (east of the
Highwood Mountains). The river quickly cut through the ridge and
created the present day canyon of the Missouri. This lake may
have risen and subsided many times with each advance of the ice.
The rising and falling shorelines have apparently been obliterated by
later advances of the glaciers. The Shonkin Sag is so deeply cut
into hard rocks that it must have been an active overflow channel for
many thousands of years—perhaps during several Ice Ages.
| Waypoint | km | mi | Lat | Long |
|---|---|---|---|---|
| Start, Fort Benton | 0.00 | 0.00 | N47° 48.96' | W110° 40.12' |
| Rural Road (right turn) | 11.3 | 7.0 | N47° 53.04' | W110° 35.14' |
Bodmer Overlooksite of famous 1832 paintings |
17.7 | 11.0 | N47° 52.29' | W110° 30.79' |
| Local Road (right turn) | 32.0 | 19.9 | N47° 55.82' | W110° 30.59' |
Marias River Overlookmerging of Marias, Teton, and Missouri |
33.3 | 20.7 | N47° 55.55' | W110° 29.77' |
Loma Overlooknew Missouri Valley |
40.1 | 24.9 | N47° 58.50' | W110° 29.90' |
| Rural Road (left turn) | 66.0 | 41.0 | N48° 6.21' | W110° 14.59' |
Big Sandy Overlooka small hill above the valley |
67.9 | 42.2 | N48° 7.24' | W110° 14.26' |
| End, Big Sandy | 82.5 | 51.3 | N48° 16.59' | W110° 7.02' |