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Geology of the Mt. Princeton Area
Some areas around Mt. Princeton are composed of granite and calcite.
The granite is a different composition from that of the Pikes Peak massif,
being primarily a mix of quartz monzonite (quartz, triclinic feldspars
(sodium, potassium, and calcium aluminum silicates), and mica. When
the granite contains very little mica, it tends to be very hard, and large
rocks, giant boulders, and even solid granite cliffs are the rule.
When the granite contains quite a bit of mica, the granite tends to break
up quite easily into smaller pieces. The calcite can be a flaky,
white rock, which can break apart easily and turn into a fine white powdery
soil. This calcite is what gives the lower southeast slopes of Mt.
Princeton (in and near the hot springs) their white color. This area
is known as the Chalk Cliffs.
Steep cliffs in this area contain a
curious mixture of fine powdery soil, small chunks of decomposed granite,
and large rocks and boulders. When an especially heavy rain occurs, the
soil can become saturated quickly and will begin to flow downhill.
The embedded rocks and boulders then will be loosened and either flow (on
gentler slopes) or tumble (on steeper slopes) downhill. These rock
and mudslides can develop very quickly. Once the flows and slides
cease moving and drier weather prevails, the "slop" sets up like concrete.
Two troublesome areas exist on CR 306 and 162. On CR 306
(see map) between
the Cottonwood Pass Hot Springs Resort and one of our spotters, the terrain
on the north side of the valley is particularly steep right
down to the road. On the evening of 22 July, there could have been
between 3 and 4 inches of rain in an hour, along with large volumes of
small hail on the slopes. There were several massive rock and mudslides
in a one-mile long stretch. The debris was up to 15 feet deep on
the highway. Looking again at the mountainside north of CR 306, we
see steep slopes consisting of soil, pebbles, rocks, and boulders.
Cottonwood Canyon, Looking North
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Cottonwood Canyon,
Looking North
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County Road (CR) 306, Looking East *
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The
landslide covered the road. Once the debris hits the guard
rails, it is diverted downhill along the roadway.
The most life threatening event during
the landslide was when a minivan and camper were inundated with
rocks and mud. An elderly couple got
stuck in their van in the debris, and were nearly crushed in their vehicle. They
had some scratches and minor hypothermia. It took around two weeks to completely clear the road.
The following are some images of the trapped van and clean up. Photos
are on CR 306, between 6 and 7 miles west southwest of Buena Vista.
(*Photo Credits - C. Hasselbrink, Chaffee County EM )
Van and Camper in Mud
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From Van - Looking East
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Looking West
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Looking Down on Van
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Van in Mud - View from Road
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Bulldozer Digs out Debris
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Van in Debris - Looking East
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Digging out the Road - note Yellow Line
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Almost to the Van...
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Road Dug out from Mudslide - Notice Debris on Either side
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Mud and Debris on Guardrail
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The debris that made
it over the guard rails tumbled into Cottonwood Creek. After
the creek gets "dammed up" for a time, it cuts through the debris.
It took Cottonwood Creek several hours to cut completely through the debris.
The spotters property was also hard hit. Rock and mud flowed and tumbled
down the mountainside toward his home and outbuildings. The
original mountain road (Stage Road) which came down from the summit of
Cottonwood Pass in the 1800s, runs through his property. Rock and Mud flows
and deep channels ran across the old road, and then tumbled onto CR 306
below.
Cottonwood Canyon, North Side
(T. Magnuson)
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Cottonwood Canyon, North Side
(W. Fortune)
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The guard rails along CR 306 kept much of the larger rocks
and tree debris banked up on the road, and allowed the debris to flow downhill
on the highway. Therefore, there was debris along a one-mile stretch of the roadway.
To give some perspective,
spotter said that a rock and mudslide of this magnitude has never occurred
at his place (built in 1970).
On CR 162 (see map), west of the Mt. Princeton
Hot Springs Pools, there is a very dangerous dip in the road. The
county has tried all sorts of tricks to make this dip safe: culvert,
unpaved dip, etc. This configuration is the best solution. Looking
down toward Chalk Creek the unsorted debris cascades into the creek.
Entering "The Dip" on CR 162, looking Southwest
(K. Craven)
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Looking down The Dip into Chalk Creek
(K. Craven)
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Looking up The Dip, to the Chalk Cliffs
(K. Craven)
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Our spotter who lives next to the dip, says that in the 22 years he has
lived there, the dip has to be cleared 2 to 3 times a year. He has
seen minor blockage of the dip, and rarely, large boulders flying across
the dip at 40 mph! The last close call at the dip occurred in 2000,
when a motorist tried to go through the debris during a heavy rain.
He got out of his truck but left a passenger in the vehicle, which then
tumbled down into the creek bed. Fortunately, she survived. There
are other flow and slide areas upvalley between the dip and an area called
Alpine. On CR 162 at Cascade Falls, you can see the steep,
unstable cut along the roadside.
Looking East on CR 162
(T. Magnuson)
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