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<br />NWS Pueblo. CO, ChalTee Couuty Rock and Mudslides - July 22,2002
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<br />NOAA's National Weather Service Weather Forecast Office
<br />Pueblo, CO
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<br />Chaffee County Rcx:k and Mudslides ~ July 22,2002
<br />Cottonwood Pass Road (County Road 306) and County Road 162 ("The Dip.)
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<br />t. .L. _, 'i' Hl. Between 6:00 p.m. and 7:00 p,m. on 22 July 2002 (0000.0100
<br />~-L~ . . r! UTe 23 July). a rock f mudslide occurred on the Cononwood
<br />3..:---'--~".,.L ; 11 ,.~' _ "-l Pass Road (County Road 306) In the yaney norlh of MI
<br />It ".;f.,..J.\., ~rA"tt\Jfl~} Princeton (14,197'). west southwest of Buena VISta. CoIotado
<br />r.L...&~,'.;J';~di ~_: \ County Road 162,1n IhevalleysoulholMI Pnncelon,alsohad
<br />~!~ a1') 1 : ,,'slgnlficant rainfall and eltpenenced rock and mudslides as well
<br />~ .......-:f...... . ...;~- {tr' ~ltf~ One main reason for these rock and mudslides IS lhe type 01
<br />r1J....~'~. s ~--:.!! 1 ~ SOils and rock In thiS regIOn
<br />,,: ~lSAeElTr.p~~.. .
<br />~;- "(:'f:~;..t'" r .- (ClICk Map for Larger VIew)
<br />.... ...- -,1\ ......t:'..
<br />")~~,j;?r,, e.-:>' . '1::1l-
<br />,. -\ ~
<br />"The '0....
<br />~.~ -....,-.t-If....
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<br />Geology of the Mt. Princeton Area
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<br />Some areas around Mt. Princeton are composed of granite and calcite. The granite IS a different
<br />composition from that 01 the Pikes Peak masslr, being primarily a mix or Quartz monzonite (Quartz,
<br />tricllnic feldspars (SOdium, potassium, aOO calcium aluminum silicates), and mica. When the granite
<br />contains very liltte mica, it tends to be very hard, and large rocks. giant boulders, and even soIKl
<br />granite cliffs are the rule. When the granite contains Quite a bit of mica. the granite tends to break up
<br />Quite easily into smaller pieceS. The calCIte can be a flaky, white rock, which can break apart easily
<br />and lurn into a fine white powdery soil. ThiS calcite is what gives the lower soytheast slopes of Mt.
<br />Princeton (in and near the hol springS) their white color. This area is known as the Chalk Cliffs.
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<br />Steep cliffs in Ihis area contain a curious mixture 01 fine powdery soil, small chunks 01 decomposed
<br />granite, and large rocks and bouldms. When an especially heavy rain OCQJrs, the soil can become
<br />salurated Quickly and will begin to flow downhill. The embedded rOCks and boulders then will be
<br />lOosened and either flow (on gentler slopes) or lumble (on steeper slopes) downhill. These rOCk and
<br />mudslides can develop very Quickly. Once the flows and slides cease moving and dner weather
<br />prevails, the .slop. sets up like conaete.
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<br />Two troublesome areas exist on CR 306 and 162. On CR 306 (aee map) between the Cottonwood
<br />Pass Hol Springs Resort and one of our spoilers, the terrain on the north side 01 the valley is
<br />particularly steep right down 10 the road. On the evening of 22 July. Ihere could have been between 3
<br />and 4 inches of rain in an hour, along wllh large volumes of small hail on the slopes. There were
<br />several massive rod<. and mudslKles in a one-mile long stretch. The debris was up 10 15 feet deep on
<br />the highway. looking again at the mountainSKle north of CR 306, we see steep slopes c:onsisllng of
<br />soil, pebbles. rOCks, and boulders.
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<br />Cottonwood Canyon, Looking
<br />NOflh
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<br />County Road (CR) 306, Looking
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<br />Coltonwood Canyon,
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<br />http://www .crh.noaa.gov/pub/c",cntslmuuslidcs/mudslidcs.php
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<br />7/23/2007
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