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<br />..RUEDI DAM AND RESERVOIR, COLO.
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<br />Designs fire subject to modification us additional information becomes
<br />:l\'aiJable. ...J"'
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<br />aeolo9Y , .
<br />Preliminary g-eologic inyest.igat.ions in the dam 8n,tl res~rvoir area.
<br />were made ill ID46 and IV4S. The: Frying-pan RIver, 111 floWIng
<br />westward to meet, the Roaring' Fork Riyer, crosses a. series of forma-
<br />tions of Paleozoic uO'e. The damsite occupies fI. narrow g-org-e cut
<br />illto red-colored santGtones and shales, the upper part. of t.he. .Maroon
<br />fOl'lI1ntion of Pennsyh"nniun ag-e. These Illas~ive strahl dip steeply
<br />dowllstream due to faulting anu folding- in the IOI~a] firen. The entire
<br />)la1'oon formation as exposed in the vil.:.inity appelU's to be about 2,500
<br />feet t.hick, wit,h some 1,000 feet of upper re,d sandstones underlain by
<br />]~OU() feet of alt.ernating buff-colored siltstones and lil11e~tolle5, in t,urn
<br />resting on fl berl of gyp:mm exceeding rA~O fe-et in thirknesH. The
<br />regional structure is t.lnlt of :1 pllll1g-ing: anticline. t.he rin~r l'.lltting :t
<br />steep canyon across the upper red sandstone hogback. with the hasa.]
<br />gypsum being- exposed in the resen'oir 01' central anticlinal area near'
<br />Rllerli. The g'ypsum hed necessarily underlies the dam at a depth of
<br />about 1,000 feet. Tlle intervening lilllestones will O('C,llr nt, le!:is depth.
<br />As a matter of judgm,ent, the proposed re8el",oir will prove satisfac-
<br />tory fl'om a seepDl!e standpoint,~ but this cOlJelusion must be cheekerl
<br />by deep drilling and detnilf'd gcologic:d work
<br />The immediate fOllndat.ion for the dalll consists of lllnssi\"e saIld-
<br />stnne strata (J to 4- feet. thiek) \\"ij It illh:>n'cnillg' ~haIe JnYf'l"s. These
<br />beds Llip down:;t.renm :~r)o to 400 Hlltl S1 rike noj.-thwe3tel"iy 400. The
<br />l'lll:k is cOilsiderably jointed. One ~ystel1l strikes l\OrtIH~ast. :.tHe! dips
<br />ROO to DOo to the SOllt,heast,; t.he. other strikes nortll\yest., dipping 400
<br />to 540 to the northeast. A fault of unknown churaetf'J', dipping 700
<br />downstream, CI'osses t.he e:lllyon illuncdintely upst.l'eillTl frolH t.IH~ diun.
<br />The extent, and sig-nific311(,8 of this fault mnst. be determined before
<br />the geolog-ica 1 sitl1fition is t.horollghly lwderstoocl.
<br />Ei~ht explorntory holes \\"ere ,lrilled in W+S at the damsite, The
<br />foundation rocks appear fldeql1atel~~ stable for construct.ion of an
<br />earth dam. Howc\'er, furt.her drilling- is required to e\-aluate fully
<br />reservoir nnd dll.msite seepage conditions, 'Vater-pressure tests
<br />indicate 1,hat. ~ronting- will he necessary to cont.rol seepage of wat.er
<br />.under and nrou1Hl the (lam.. .
<br />Prospecting and testing of tllC seveI'lll t.vpes of n\"nilnhI~' iill1te'i:ials
<br />will be necessary prior to design nlltl const.ructioll. It is prohable t,hat
<br />sfltisfnctory dp,po:iits of silt, sanll. fina gravel call be lOl:ated in the
<br />]'eservoir f1!'ea for impelTj(lllS, semlPt'rvious, and perri(HlS emufrnk-
<br />rnents r!?qmred for the proposed earth dam. GTll\"els in the vnrious
<br />ri\'er ter:races a~d in the l'iyer channel, derived ill pal't.,frQm granitic
<br />and met:lIn~rphlc ar~as in the upper reaches of the FryiJlgpan Ri\rer,
<br />pl'ohably wIll .i.Je slIltable for concr.ete a::r~l'egat(l. Clitfs of .Maroon
<br />_~l.lndstones whIch are exposed downst.renm fl'nm the tlalllsit.e appear
<br />,suitable for ripr~p.
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<br />Construction a,spr.ct8
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<br />Constl'uc~io~f the dam and resf'1'\'oir. wil~ r~qllil'~ the 3. equisit.i?n
<br />of ubont l.';IO()~l'eS of lml.\l~ most. of WhlCh IS In pl'l\"flte ownersll1p.
<br />The- :1l'ea lJlclllde.o:; about. :!r,o 3(Te~ of farmlands \\"hich nJ'c devoted
<br />largely to produdion of nat.i\'e hay under irdgation. The re.maining
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