Geology of Idaho
The Northern Rockies
Northern Rockies
Basin & Range
Middle Rockies
The 3 mountainous regions of Idaho
Northern Rockies
This is the largest mountainous area of
Idaho covering about ½ of the state
<Coeur d’Alene R.
<Clearwater R.
<Sawtooth R >
<Salmon River R.
<Lemhi R.
<Lost River R.
<Cabinet R.Selkirk R. >
Mountain ranges of the N. Rockies
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Bitterroots form part of the
boundary with Montana and part
of the U.S. Continental Divide
12,655 feet>
The Lost River Range has Idaho’s highest point, Mt. Borah, rising 12,655 feet
Lost River Range
• Lost River Range has several peaks over 10,000 feet
• Towering over Hell’s Canyon on the western edge of Idaho is another spectacular set (nearly 9000 feet) of peaks………..
Seven Devils Range
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Longer than the Snake?
Rivers flowing from the NR
carry runoff from rain and snow.
The Salmon River, flowing
420 miles, is the longest river in
Idaho.
• The Salmon runs from Stanley Basin at the foot of Galena Pass, through the Northern Rockies and joining the Snake River 40 miles south of Lewiston
The River of No Return
Named for the deeply eroded valleys and the boiling rapids experienced by rafters
Feferal recognition of the magnificence of this region in isolation, beauty, and uniqueness
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1. Kootenai River
2. Pend Oreille River
3. Priest River
4. Coeur d’Alene River
5. St. Joe River
6. St. Maries River
7. Clearwater River
8. Lochsa River
9. Selway River
10. Salmon River
11. Payette River
12. Boise River
13. Lost Rivers
Rivers of the Northern Rockies
River valleys provide transportation routes
The rivers themselves may become routes of
transport, too!
Dworshak Dam
Dams on some rivers provide opportunities for recreation, irrigation, hydroelectric power, and
flood control
717 feet high and over a half mile long!
• The Purcell Lobe of the Cordilleran Ice Sheet moved down into the Panhandle of Idaho and created lakes
Glacially scoured lakes
Lake Pend Oreille Priest Lake
Glacially dammed by glacial moraines blocking valleys
Spirit Lake
Hauser Lake
Hayden Lake
Glacially dammed
Lake Coeur d’Alene
Alpine glaciers left lakes, too!
Glacially scoured lakesRedfish Lake
Payette Lake
Geologic Origins
• Volcanic activity
• Folding and faulting
• Glaciation
• Water erosion
100 million years ago the 2nd largest batholith in the world formed in Idaho
A large, granitic formation that is the core of the Northern Rocky Mts.
Evidence of the heat that remains
With the magma came many minerals that later formed valuable metal
ores like gold, silver, and lead, as well as quartz
• In some places, pressures within the earth caused layers in the crust of the earth to fold or crack (fault).
• This created mountain ridges and valleys.
Examples of fault block mountains
Thrust fault scarp near Stanley, up and over the other side of the fault line
Glaciation in Idaho• 15,000 years ago ice covered all of NR
that was below 8000 feet in elevation
• 1000’s of feet thick carving/scouring the landscape of NR in many places
• Great weight caused glacial ice to move
• As they moved down V river valleys they remodeled them into U glacier valleys
• Left piles of debris called moraines
• Left moraine dams and flat valley floors
• Left many alpine features in the NR
Pend Oreille - Carved by ice
Coeur d’Alene – River valley blocked by terminal moraine
Ross Point Hill (terminal moraine) overlooking Rathdrum Prairie (glacial flood deposits)
Water erosion figures into the geologic landforms of the N. Rockies leaving many V- shaped valleys
Alluvial fans often formed at the openings of the v-
shaped valleys
Climate - precipitation
• Wetter than the rest of the state
• Moisture forced out as air force to rise over the Rockies– 20 inches in Post Falls– 40 inches in Wallace/Mullan area
• Precipitation in Panhandle = 30”
• Southcentral = 7-26
• Snowfall heavy because of elevation
This is caused by moist air which flows through the Columbia Gorge in the Cascades from the Pacific and to the Northern Rockies. It then is wrung dry as it climbs the face of the Rockies.
return
It is approximately 60-75” annually in most places; McCall = 151”;Stanley, Challis = 94”
return
Climate - temperature
• Low winter average = 20 degrees• Southcentral average = 10 degrees• Summer average = 84 degrees in the
panhandle, 88 in southcentral
back
Northern Rockies are the most heavily forested part of Idaho.
Idaho is the most forested Rocky Mt. state!
Mountains and forests of the West
Red cedar, Douglas fir, hemlock, spruce, lodgepole pine, and Western white pine
provide a rich resource to Idaho
White pine (Idaho state tree) – 180 feet tall and
2-4 feet in diameter
The largest stand of white pine in the world is located
here, in the St. Joe National Forest
The forest understory includes syringa, ninebark, Oregon grape, wild rose, huckleberry, and snowberry (shown here).
End of the day, end of the presentation!
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