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<br />. ," <br /> <br />( <br /> <br />\. <br />\ <br /> <br />18 <br /> <br />Gaylord y. SkogE'rbOt' <br /> <br />DlftOlCIUr <br />.A ....",." <br />~ ..J3::Za~ <br /> <br />UTAH . p,~E7'" <br />I A<tho; J(.:";" COLORADO <br />Copitol ::'f",f"":-n:~O~CI' <br />"E VAOA . r~t' II" I BloCII cCIflJOl' <br />I "l!. rnon dl t' j "of ,h, lJ'ItlfMlotI <br /> <br />'- j. ~~~~: ~;.r:"i :.. ~o~o;b~~.' I t.YUCCCI h::nfftOfl <br />" Ion.... f"pmnbOw" .not man not mon <br />.. -r-po,1t · "I.' JHo~"W";4 _M.sa yt,'" <br />, .. _ _ ~J_.. "III man not ".11 ...- <br />" O..nd -.-. --.- .--.._U_U-.'f <br />" , CO""," . ,NawtIG. .&".e ,ytM <br />", . 1 ~... C.";~~ ""'" CPtac~'.= ..- <br />. t"'",,\ .. .. "..II,. li!i! m.n <br />, J ", Mtman~'" . <br />CAt."ORNIA ":, Sunil' ..Wupotkl. I' <br />.,,, craft, not met" :s:::.~on <br />" T.,'tOO' e"".,. . I <br />Jo.'.huot'"'~ natmo"' PIO'''''''' ~ tlmorro I <br />"at mon . ~"jfl'd net "'Of' <br />Qqo Montaurno fOfut ,..E'If' M[JeICO <br />"'. .,..' caltle nGt par' I <br />) nat~ ' <br /> <br />_.. (AIIIZONA .~~':'" 0110 'Mf \, <br />--,) . c... ,fond. · dwrt IIl"It.. <br />n......... I <br />. o,to" pi.,. 1'\0' "'01' <br />" eochl' <br />........... noJ.J!:"" 5....,. I <br />.~. ."o'mon ~.._.._..-.J <br />ME>ICO .......... I f"---, <br />_u_u-L... <br /> <br />Fig. J. NatlfJnf" P~"k,. an" NII"d""' Monumenr.t 'n ,II.. ("OlfJrtlf'fJ IUI'" Bmdn. <br /> <br />LOWER C01.0RADO RIVER BASIN <br /> <br />PI, v~/(I"r/I"/IY <br />The Lower Colorado Region i5 com!,osed or a com!,lcK or !,Iatenll~. mOllnlnin~. <br />canyons. deserls. and plains. with elevations ranging rrom 75 reet ahove sea level year <br />Yuma. Arizona, to over 12,600 reel ahove sea level at Humphreys Peak near Fla~staft', <br />Arizona. The topography takes in virtllally every rorm and degree rrom level plams to <br />.precipitous mountains and canyons between these elevation extremes. . <br />Similarly, the geology of the Region includes 8 ~road spectrum ~r sedimentary, meta- <br />morphic and igneous rocks which !,rodu~ a wide var..e~y or sOils Ioc:ally an~ along <br />stream counes. In short, the princi!,al phYSical characterIStiCs or the Region are ItS great <br />variety or land rorms, to!'ollrn!'hy and geolollY., . <br />Many or the slreall1~.trihulU"y tothc ('olorndo River head 111 narrow ~anyons an~ run <br />through deeply-cut gorges, The Cohlrudo Riv~r hccal11e.athrough-~loWll1g strell~ m the <br />late Cenozoic time. Downcutting by the fiver and ItS tributaries resulted In .dee~ <br />entrenchment or the entire system creating spectacular canyons, most notable of wh.Jeh "5 <br />the Grand Canyon or the Colorado, All runolT rrom the high ~Iatealls and mountal~s ~n <br />the Lower Colorado Rcgion is tributary to the Colorado, Little Colorado .and ~Irgm <br />Rivers. The Colorado and Virgin Rivers are perennial; all other streams are mtermlttent <br />at their connuence with the Colorado River except for ~hort reaches downstrea.m from <br />springs such as Blue Spring and those in Havasu Canyon and near St J~hns, Arizona. <br /> <br />.~ <br /> <br />..........,...,...-- <br /> <br />~ <br /> <br />._ ."T ,_ -...-_. ~.,.~ <br /> <br />'~_.."_'_' ~,.......".,.... ......[.' _ _, '" _,-~ .IP' . <br /> <br />The Phy.~/cal Enl'/ronmE'nt of thE' Colorado Rh'"r Ba.dn <br /> <br />19 <br /> <br />The storage and movement of ground water in sedimentary rocks are controlled by <br />regional structure or the basins and upwarps. Storage and movement in alluvial hasins <br />are rrequently controlled by valley plugs created by lava nOW5, tectonic movement and <br />nearly impervious alluvial deposits. The main areas or rechargc are on the highlands, on <br />the upwarps, and along the structural divides. Movement of ground water is downdip <br />from the highlands toward the pcrennial streams (Lower Colorado Region State-Federal <br />Interagency Group, 1971). <br /> <br />ClimatE' <br /> <br />The Lower Colorado Region's climate varies widely because or a large difference in <br />elevation, a considerable range in latitude, and the distribution or mountain range5 and <br />highlands. Generally, the climate or the more densely !'o!'ulated areas or the Region. such' <br />as Las Vegas. Nevada, and Phoenix, Tuscon and Yuma. Arizona. is characterized hy <br />mild tei warm annual temperaturcs, low to moderate humidity and low annual preci!,i- <br />tation. Summer tempcratures often reach IOO"F and abovc. Rainfall i~ predominantly in <br />the form or thunder showers which are sometimes very inlense and !,roduce nash nood. <br />inllloc;llIy. EKce!'t in the mountains. snow is rare and short-lived. Annual rrost-free days <br />in the lower dcsert range rrom over 270 days to year-long. Yuma. Ari/ona has eXflCri- <br />eneed several yenrs in succession without n killing fmst. Thesc climatic ractors are very <br />favllfnhlc 10 Ihe irrigalcd a!:rieuhurc conecnlraled in the lowcr clevalions. <br />In conlr..st, such cilies as Sl. Gcorge. Ulah. Winslow and lIolhrook. Arizona and <br />Gallup, New MeKico, have more or a rour-season climate with shorter rrost-rree periods <br />and colder winter months. FlagstalT. ArilOna. and other cities in mountains, rimrock, and <br />pl~teall locations have suhstantially shorter frost-free periods. mild summers, cold <br />wmlers ;lnd considerahly more rain and snow. Most of the recharge to ground water and <br />the surface runoff in the LCRB results from precipitation in the high mountainous areas. <br />VI' to 30 inches or !,reci!,illltion a year lire recorded, much or ,,'hich i~ in the rorm or <br />~noW (Lowcr ('olorado RCllion Stnlc Fedcrulln1ernllcncy GWIII'. 1971) <br /> <br />Watl'r resnllrce.~ <br /> <br />~he Lower Colorado River Basin ptohably comes closer to using the lasl drop or <br />available water for man's needs than any other area in the U.S.A. These water supplies <br />are also a~ong the most regulat~d and metered in the Nation. Despite the most rrugal <br />use. recycling and the hIghly effiCient rcgulation or water, the lCR B is mining water each <br />year that cannol. be, re!,Ie,nished by natural recharge ror many decades. Virtually every <br />sector or the Region s soclo-economic structure is heing sustained in some dq~rcc hy the <br />overdraft of ground waleI'. <br />Three main sources of water were availahle in 1965 flowcr Colorado Region Slate- <br />Federal Interagency Group. 1971): (a) enlitlcmenlto 11 mllr or Colorado River waleI' hy <br />a body of .Iaw rderre~ ~o as Ihe, "law or the River"; (h) local runolT amounting to <br />3.12 mar Orlglll;'.'lIlg wlthlll the regIOnal boundaries and (cl lOCAl ground water reserve~. <br />The 3.1 mar enllllement rrom the Colorado Rivcr has not been rully utili/cd because of <br />Ihe lack or conveyance racilities to tran~!,ort water 10 Ihe areAS or heAVY demand. At-out <br />8,2 mar were wilhdrawn from surrace- and ground-water sources in 1965. Apl'roKimately <br /> <br />~. <br /> <br />~ ..-~~ <br /> <br />- ,"" ..;:w;~~.. , -'-'~. .~.~ ~-..~~.. '~'- -~ -,..".,.~ --"~" '-'- ~. - .... ~.. <br />