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!