Formation of the Gorge and Falls

Formation of the Gorge and Falls (HM1K9F)

Location: Great Falls, MT 59404 Cascade County
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Country: United States of America
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N 47° 34.098', W 111° 7.234'

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... the rocks seems to be most happily fixed to present a sheet of the whitest beaten froath for 200 yards in length and about 80 feet perpendicular. — Meriwether Lewis, June 13, 1805

The Great Falls of the Missouri River was first described in writing by Meriwether Lewis on June 13, 1805. In 1915, the upper part of the falls was inundated by Ryan Dam to produce electricity. These photos are views of the falls before the dam was constructed.

... the irregular and somewhat projecting rocks below receives the water in it's passage down and brakes it into a perfect white foam which assumes a thousand foams ...
— Meriwether Lewis, June 13, 1805

The explorers were very impressed with the narrowness of the Missouri gorge and the falls:
... I beheld those Cateracts with astonishment the whole of the water of this great river Confined in a Channel of 280 yards and pitching over a rock of 97 feet ... — William Clark, viewing the falls for the first time (June 17, 1805)

Natural waterfalls need three things:

  1. Plenty of water at least seasonally

  2. A river or stream that is cutting down through the landscape due to some recent change in the the drainage. In this area, the Missouri River was apparently forced out of its old channel when a continental ice sheet moved into northern Montana during the last ice age. The displaced river went to work cutting a new channel, and it has not yet finished the job. In time, it will look more like the Missouri River valley upstream and downstream of the gorge. The river will meander across a broader valley with fewer waterfalls.

  3. A layer of rock that resists erosion more than the rocks above or below it. Hard sandstones are interlayered here with softer mudstones. As the river cuts its gorge, it gets "hung up" on the resistant sandstone layers, forming falls.
HM NumberHM1K9F
Series This marker is part of the Lewis & Clark Expedition series
Marker ConditionNo reports yet
Date Added Wednesday, April 29th, 2015 at 6:01pm PDT -07:00
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Locationbig map
UTM (WGS84 Datum)12T E 490931 N 5268327
Decimal Degrees47.56830000, -111.12056667
Degrees and Decimal MinutesN 47° 34.098', W 111° 7.234'
Degrees, Minutes and Seconds47° 34' 5.88" N, 111° 7' 14.04" W
Driving DirectionsGoogle Maps
Area Code(s)406
Closest Postal AddressAt or near 173 Ryan Dam Rd, Great Falls MT 59404, US
Alternative Maps Google Maps, MapQuest, Bing Maps, Yahoo Maps, MSR Maps, OpenCycleMap, MyTopo Maps, OpenStreetMap

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