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<br />NATURAL FACTORS
<br />ThundcrSLOnns in aridt'<llvirnnrilcllts. such as inthe vicslernpart
<br />or the VeOL stndy llnit. can,e large sllspended-sedhTlenlload~
<br />in streams, Nalurill hOI springs contrihufe about .100~OOO tons
<br />of'di,~olvccl :-;olids( 15 pt~n.:cnt of the total-salinity') annoalJyt'O
<br />thc"stteatn'-.; in the b;;'lsill
<br />..-- - - - . - -- --
<br />
<br />Physiography and Climate
<br />
<br />Ihe pl1\"I(\~r;lpll\' I" charac!l'r1/L';1 h\ l1i!..!h !1\{llllll<lil1,\ illlhl.,' ('a~l
<br />~~H1d pla\c:l"ll<.; ;t;ld \,:tlk:~... in tile we,,\. 1<\'{lI~hY,>I()grapl1il' prll\'inCl"-'
<br />cJtll\ldc llw ';lud: utili: ll1l' SOllllll'1'Il Rud;y \l\llllllaill<'; III thl' ca'ill'rll
<br />,-,ran ;llld Illl' ('nlllrad(\ 1)1a1L':HI III !he Wl''\!l'rrl p:\rl (Iig. I). I'he l'a'i1"
<br />,'Ill ;tlld "UIlllllTll h(\lllldariL''' o( 111l' "lud: L11l11 !'ll!lm\ 111\' Corllill(,ll-
<br />ul Di\ id" Ikcau,>l' uf largl' dift('rl'lll.l'.... In altiludl' IWI\\,'CCIl (llC
<br />phy....lngr;lplw.: [)to\ Il1l.l...... l.jinwll: \;tl'ic' ....lIh....wlllially Ik'l\\'l'l'llthl'
<br />l.';l....tnll ;1l1d \\'l'"lnn parh or till' ha....itl. Daily. 1l1(llllhly. alld anuual
<br />,1\l'r,I.~l' 1l'1ll11lT;1l1In..... arc 11Ighe"l al till' Invvl'r dllitudl'" 101111.: Wl'q
<br />('lirl1<1tl' l'h;1I1~t'" Irlllll ;dpilll' l,.;ollditioll.... ill tIll' l';hl ttl "l'll1i,lrid tn
<br />,Ind l'(llldilillll" illlhc \\l'''1. PrcCipllatlOll gl'lll'r;dly r:\llgl'" t"rurl1
<br />j() irll"ht,....llr Illllrl' pl'r Vl'ar in the l'a-.;\l..'nl P;lrl Ill' tlK' h;l"illln ie"s
<br />IlIall I () Illl.lil'.... jll'l :l'al ill rhe \\"f,.'''h.:m part 01 Ihe basl1l (Ii~. ~),
<br />
<br />
<br />Oto 10
<br />J >10to20
<br />1 >20t030
<br />- >30t040
<br />- >40ormore
<br />
<br />10 40MIUS
<br />
<br />o 20 40KIWMHfAS
<br />
<br />- --- ---
<br />Figure 2. Aver<lge annual pWClpltation (in Incheslln the Upper
<br />Colorado Hiver Baslll SllJdy unit (Colorado Clmln1e Center. 19134)
<br />
<br />Geology and Soils
<br />rill' u11llt'rly ill~ hl't1I11C"- !Ilthl' ....Iudy 1I11ill.(\1I....i..;t.... prl'dolllill;lIllly'
<br />III cr:....tallllle ,lIld ,,"'dillll'lllary rock". .-\11ll\ iUIl1. l'()r,....l'\lill~ or"
<br />....tl\';lllI. Lind"lidc. Inr;Kt.'. and ~1;H'I;lIlkp(hih, i.... prl''-enl ill valky"
<br />tl1rllllglltllll the \1;1'-111. [Illi~ur('~, llll' hl'drm'h .~l'ol()g: ha'- hl'l'1l
<br />di\ 1{J<,:d illlrl i~lh'llll" and 1lll'la1l1orpllH: rol''''': '-l'dil111'llli\1"\ roc"-"
<br />I tUIIIll'i' ~IJhdi\l,-illll'- llf Ihi" tUll! \\-Crl' l1ldtit' If ~l prcdolllin;lnt nll'k
<br />l~ I',' (11' l.:lrl'OIl;lll', ,-;llllI-.IOl1t'. m ..;halt- \l';l" Idl'tllllled 1: inlru"ivl'
<br />rnd,,, (l)llt'll a,-,-ol'I:lll'd \~'ith Illlllt'r;ll dL'Jl()"Il'-l: ;lIld vl1!c;lllic I'Ock,-,
<br />
<br />Wl'<llllL'ring o!" the diffl'rcllI gc()lt)gie uni!" alTccts water-quality
<br />L'tmdiliollS in the >;Iudy unit. The igncolls and metamorphic rocks
<br />of lhe upper basill contribule fewer solutes to the streams than do
<br />th1..' ..;cdimclltary rock..; of till' lower basill. At higher altitudes ill the
<br />lippeI' basin. cxpo'ied igncoll'i. metamorphic. and volcanic rocks arc
<br />fairly' re"istant to wCi.lIhering. and tlw'i 'ialinil)' in the \-vater is low ill
<br />1I1l''iC upper s!ream n:acllC'i. Also. llIincr<llizl'd areas ill the upper
<br />ha'-1I1 L'orllributc Iran~ c1emcnts 10 the 'iUrraCC and ground walers.
<br />
<br />\\/hl' 11 the ..;lJ\',Ulh C01l1C in contact with outcrops or ,>cdink'ntal)
<br />rock" ill till' middle alld Im\'L'I" reachc" of the hasin. "alinitv ill the
<br />willl:r lllcrease..;. III the more arid clilll<1le al lower ahitudL'''; ill the
<br />w(''llerll part or lhe hasln. prccipil<ltioll commonly is in the form
<br />l)r tl1LlIHh,'rsttlrlns. ;Uld rlll'lolf rnnll thundl'l"stmm..; can deliver largc
<br />load" or "cdilllC'llt and >;alt'> to tlw 'itrcams. In addition. evaporation
<br />in thi:.... arid L'li11late 1.:1lhallL'(''- llll' accullllllation of "ails nil the
<br />"oil. \\hicll Ihl'll can be dl'liVL'red to "trcillllS during :....tOrln runoff.
<br />Seleniu1l1 i" prc'-ent naturally in the "hale bedrock ulthc nuddk
<br />and lo\\'l'r 1\~iH:l1l~". and it ilL'cur..; in the "urhlCC and ~round water..;.
<br />
<br />Till' prc"l'lKC of lllallY 11l11ll'l"ul ....pring..; ill the "tudy \11111 also Iws
<br />,I majl)t" cfkct (Ill \)/,lIer quality. TilL: springs prinlari I)' ;Ire located ill
<br />carhonate rock unit.... ill the area ..;urrounding. (,kllwnod Spring..;.
<br />Colo. lli~..;. I dllll .I). Till' lllllleral hot springs cOIHrihutc about
<br />15 pl.TCClll of thc [olal "alinity anllually to Ihe "trcalll" ill the hasin
<br />(l .S. Ikp;ll.tllll'l1l or the l!Herio!". It)I))).
<br />
<br />Soil..; ~llso Clll ~llTl'ct wallT qualil)' hecause "oils can he a S(Hun:
<br />()f"ll"PCllikd ..;edilllcllt ,lnd "ofuhk' mated"ls (salts). Suspended
<br />";l'rlilnl~111 in "Ircanl" pn:(hmlinal1lly is a resull ofchalllll'l cl"ilSilH\
<br />,tilt! '-oil cro"ion fmm "tornl runoff Gellcrally. \llSPClldcd~...edi.ll1l'lIl
<br />cOllcelllration" 111 "treams inLTcasl' from the l'astern edge of the
<br />("olora,1\l PlaIL',HI phy\i()~rilphic province 10 till' olltllow or the
<br />ha~in al till' Coloradn-lJlah StatL' linc. Solllhle llwleriab arc added
<br />III 1111..' "lrea1lls hy "torm rlllloff.
<br />
<br />
<br />EXPLANATION
<br />
<br />Igneous and
<br />Metamorphic
<br />
<br />Sedirnentary
<br />
<br />Undivided
<br />
<br />Carbomlle
<br />
<br />Sandstone
<br />. Shale
<br />
<br />. Intrusive
<br />
<br />10 'G '.'lO'~(lfRS
<br />
<br />Volcanic
<br />
<br />- -~ - - ~
<br />Figure 3. Generalized geotogy of Ihe Upper Colorado River Basin
<br />study unit (modified from Schruben and olhers. 1974)
<br />
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