usgs pp228 henry mtns geo geography

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CONTENTS VII

Pa g eFIGURE 85. I ndex ma p showi ng th e pr i nc ipal ph y sical fea tu res of Utah an d their relation to th e H en ry M ounta ins _____ ___ 167

86. Pr ofiles of lan d (orms in th e H en r y Mountain s __ ______ ____ __ ______ _ _____ ________ _ ___ _____ _ ______ _____ __ 16987. Vertical view of th e Colorado Riv er below Hite __ _______ __________________________ ____ _____ __ ___ ____ __ __ 17188. Vi ew of an al cove arch______ __ ___ ______________________________ _________ _______ __ _________ __ ___ ___ __ 171g9. Profil es illustra ting sh ape s of laterall y cu t arches_ __ ___ _ ___ __ __ ______ __ __ ___ __ ___ ___ ______________ ____ __ 17290. V e rt i ca l vi ew of the sout h half of P esb liki Mesa _ _______________________________ ________ ___ _________ ____ 17391. Vi ews in the desert east of Mount Ellen. A, P edim ent along Seep Wash . B, Morrison-Summ ervill e esc arpment .

C, Small gravel-free pedimen ts in Entrada san ds t one. D , Trachyte Creek. above th e ranch _ _ _ ___ _________ 17692. Vi ew of Bri gha m Butt e_____ _____ ____ ___ __________ _ ____ ___ ____ _____ ________ _____ ______ __ ______ ____ __ 17793. Ver t ical view o f san d dune s in the Gr een River D ese rL _ ______ ____ ______ ___ ___ ____ _______ _____________ __ 17894. V er tical view o f Capitol Reef ____________________ ________________ ___ ___ ___ _______________ __ _____ ______ 17995. Vi ews along the hogba'Ck rid ges. A, Th e west flank of th e H enr y Mountain s structural basin. B, Th e R ee f of th e

San Rafael Swell. C I View along Hall s Creek an d th e \Va terpocket Fold_ _________________________ _____ _ 18096. Vi ew o f Boulder Canyon _______________ _____ ____________________ ___ ___ _______ _______ ________________ _ 18197 . Vertical view of th e Waterpocket Fold ________ _____________ _______ ___ _______ __________ ____ ____________ 18298. Vi ews in th e badland s and mesa areas . A, Vi ew nort h from Stephens Mesa . B. Badlands jn the Morrison

formation. C, Badlands in the upper part of the F erron s andston e_____________________ __ ______ ________ 18399. Ver t ical view of South Caineville Mesa ______________________ __ ___ _________ ___ _______________ __________ 185

100 . Badland s ruong Sa nd Creck______ ________ ____________ ______________ ___ __________ ___ __ __________ _____ _ 186101. View a cross th e head of Fourmil e CreeL ____ ______________ _ _____________________ _____________________ _ 189102. Vi ew o f a dike on East Spur, Mount Holm es__ ____ __________ ___________________ ______ ___ _____ __________ 18 9103 . Gravel-covered ped iments at th e foot of Mount Ellen. AI Birch Creek Benches. B, Dugout C ree k B enc hes_ _ 193

104 . Obliqu e view o f th e Cedar Creek Ben ch_ _____ _________________ ___ ___ ___ ___ ________________ ____ ________ 19 4105 . Obliqu e view of the benches at th e mouth of Bull Creek___ ______ _______ _____ __ ____________ __ __ _____ ____ _ 196106. Ma p and profile of Bull Creek an d tributarie s north of Fairview _________________ _______ ___ _ ____ _________ _ 197107. Ma p showing gravel deposits an d drainage in the vicinity of Trachyte ranch _____ ______ __ ____ ______________ 198108. Obliqu e view of the sou thwest s ide of Mount Hillers _______________ ___________ _ :______________ _______ ___ 200109 . })edim ent s in th e southern part of the basin. A, P ediments near th e head of Thompson Canyon. B , Pediment

near Cow Seep. C, Pediment near Lo s t Spring. D, Star Creek Benches __________ ________ _____ _________ 201110. Obliqu e view of th e southeast side of Mount Ellsworth ___________ _______ __ ________________________ ___ ___ 203111. Cr oss sect ion of a greasewood mound ___ ___ .. __ __ _________________________________ _________________ _____ 206112. Profil es acro ss Fremont Riv er to show th e amount of erosion since 1897_ ________ _______________________ ___ 208113. Vi ews of Pleasan t Creek b efore arroyo cutting an d a t present- ___ ________________ ___ __ ___ ____ __________ __ 209114. V iews of stream channels. A, 1896 channel of Fr em on t River, B, 1939 channe l of F remon t Riv er. C. McClellan

Wa sh, 55 ft below Naz er Creek. D, Two alluvia l deposits in Sw ee twater Cr eek ____ __ ______ _______________ 210115 . Map and view of th e alluvial depo sits a t Blu ev al1 ey_____ ____________ ______________ _____________ ___ ___ ___ 211116. A, Map of t he crosscut at th e Bromid e mine. B, Map of t he Kimbel-Turner mine_ _____________________ ___ 219

TABLES

Page

1. D erivation of place names in th e Henry Mountains region __ __ _______ ___________ _______________________ _____ ______ 212. Mont.hly and annua l mean temperatures at Ha n ksville, Utah, si nce 1920 _______________________ ______ _______ ______ _ 253. M on thl y and annual precipi ta t ion, in inch es , at Hank sv ille, Utah, s ince 1920 __ _____ _______________________ ___ ______ 254. Annual rainfv.ll in inches a t Giles, Rite, an d Hank sv ille, 189 5- 1938 __ __________________________ _______________ _____ 265. Some plants in th e Henry Mountains region an d th e plant formations in which they have been recogniz ed ________ __ ____ 286. Estimated volumes of some of the intru sio ns in th e H en ry Mountain s_ __ ________ ___ __________ _________ ________ ___ __ 1447. A nalyses of igneous rocks in the H enry Mountain s, Utah_ ___ ___ ___ __________ __ ___________________ _______ ________ _ 1548. Stati s t ical Rtudy of inc lusions in float in Gold Cre ek, Mount Hillers, by E. In gerson and E. F. Osborn ________ _______ __ 1619. Analyses of coal from t.he H enry ]\'Iountain s reg ion_ __________ ________ __ ______________ ________________ ______ _____ 218


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The distant Henry Mount ains, SUlTounded by dissected plateau country , "are simila r among themselves In constitutlon. They a ll exhibit dome-like uplifts; they all contain Intrusive rocks; and thcir Intrusiverocks are all o f ODe litho logic type. They are moreover quite by themselves; th e surrounding country is dissimilar In st ructure, and there is no gradatio n nor mingling o f churacte r. Thus similar and thusIsola ted It Is natural to regard the mounta ins as closely relnted in origin, to refer to their trachytes to a common source, and to look for homology in all their parts. I t was the soarch for such homology wlliCQled to the hypothesis t hat the laccollte is the domipa nt e lement o f their structu re."- G . K. GUbert, Geology of the Henry Mount ains , 1877. Photogra p h by :fairchild Aerial Survoys.


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IN T ROD UCT ION 3

Fold ing in the H e nr y M ou ntains s t ruc tur a l bas ill a ppa re n t lyhas not bee n r e newe d s ince t he bas in was fo r me d durin g la teCretaceous or ear ly Eoce ne time . Afte r t he ba s in was fo rm e d t heColo rado Pl a.teau s as a. who le, inc ludi ng t he s t r uct ural bas in ,were u plif te d . Th is uplift p rob ab ly bega n i n late E ocene toea rl y Mi orene t ime b u t was I'Cnewe d in te rmi t ten tl y th r oug h l ateT e r t iar y t ime an d pe rl .laps even in to Q uate rn a ry time . I nteg ra

tion o f the Colo r ado Ri ver system seem s to date fr om t he e arl ysttl4:,te s o f uplif t o f the Colorado Plat ea us. G len Ca n yo n, th eyo un gest o f t he canyons a long the Col o r ado Ri ve r, was cut af te rthe in t ru sions , of probab le mid-Tertiar y age, h ad form ed t heH en ry M o unta in s.

'V a t e r, a lw ay s a v ita lly importa n t reso ur ce, is sc a rce; o nl y afew s treams are perenn ial, and, exce p t fo r the Co lo rad o Ri ve r ,t he ir discha rge is s llla li and the ir flo w is ir reg ula r . Spring s arefew a nd a U are s m al l. T he H en ry Mou n t a ins s t ru c t ural b as inconta in s deep arte s ian water but t he qua nt.i ty an d qu ality arehig hl y unce r tain.

T he pr os pe cts for oil o r gas pr odu cti o n f ro m th e st ructura1bas in a re unfa vo ra b le un less t he u plift s a re re juv enate d ancie ntfo lds , in wh ich c aso so m e P enns yl vani an an d p re -P enn sy lvani a nfo r mat ions may be c u t off by ove rl a p an d p rovi de st rat ig rap h iet raps fo r the a ccumu lat ion o f pe trol e um.

Coa l o f h igh vo la til e bit umin ous ra nk is ex te nsi ve. Ther ea re m ino r fiss ure deposits o f go ld an d c op pe r in th e M ount Ellenand M ou n t P en ne iJ s tocks. Pl ace r go ld occurs i n th e fang lo me ra te de posite d b y t hose s tre a m s th a t n o w dr ain o r h a ve drain e dfr om the s t oc k s a nd a1 so in the g ra ve l terra ces al ong th e ColoradoRi ve r . Vao adi u rn depo s it s occur in t he lowe r par t o f the Morri son f or m a ti on and in t he Sh inarump con g lom e rat e . Th eseva ri ous de pos its have been extens ive ly p rospecte d b ut produ ctionhas been s ma ll.

Th e ag ri cult ure and timbe r r esou r ces of th e reg ion are no tim por tant; no d oub t t he c hie f use for the lan d w ill con t.inu e t o befo r stoc k gr azing. Th e recreat iona l possi bili t ies of th e regi onh ave n ot been deve loped .

INTRODUCTION

Th e Henry Mountains in south eastern Utah , wer evis ite d by Grov e Karl Gilb er t in 1875 a.nd 1876. Hi sreport , one of the cla ss ics o f geological literat ,ur e, wa sth e fi rs t to r ecogni ze that intru siv e bodi es ma y deformth e host rocks , an d th e firs t to show clen rly th e s ignifican ce of the evenly erod ed plains, now known as pediment s, at th e foot of de se rt mountains. Th e brillianceof Gilb ert's report h as been a cknowl edg ed by wid es pr ead in te res t manif es t ed in i t by geolo gists throughoutth e world , ass ur ed ly th e high es t form of tribute thatscien ce can pay for iUl outstanding con tribution . Fo rmor e than 60 years th e Henry Mountain s ha ve beenreferr ed to in the gco logicalliteratur e of ev ery languag ean d ar e one of th e lo caliti es mo st wid ely known to th escien ce. No geologis t Deeds t o be introduced to them.

Th e opportunit y to make a mod ern survey of theregi on aro se in th e course of th e G eological Survey 'sprogram for geo logi c mapping of southeastern Utah .Th e pr ese nt report givin g the resul ts of tb e s urvey ison e of a seri es of G eological Survey r eports (Bull. 793,806-0,819, 841 , 863, 852 , 908, 951, and Prof. Papers

164 and 188), mo stly based on plan e-table surv eying,that now covers pra ctically all of th e southenstern partof th e s tate.

Th e ar ea described in thi s r eport (fig. I ) includes theHenry Mountains iUld all of the s urrounding s tructuralbasin , except th e s outh ernmo st part that lies south

of th e Colorado Riv er . I t includ es part s of Emery,Wayn e, Garfield , and Ka n e Counti es. Th e area isbound ed on th e eas t by th e Colorado River and itstributary, th e Dirty D evil River , and on the westby th e Waterpock et I'old and Capitol R eef. I t ncludesa small part of th e Sa n Rafael Swell at th e north an dexte nds south to th e plac e wher e ti, e Waterpo cke t Foldis cro ssed by th e Colorado Riv er. Altog e th er th ear ea em brac es about 2,500 sq mi of which th e HenryMountain s constitute about 100 sq mi (pI. 2 ) . I t lieswi thin and is typical of the Canyon Land s sectionof the Colorado Pla te au s, an area that ev en today isdifficult of acc ess. Mod ern m ethods of transportation

hav e barely pen etr a te d th e region an d it persists as aroadl ess frontier , th e larg es t primitive Ilrea within theUnited St a tes.

Early explorers who sought rou tes for transcontinental railroads avoid ed thi s arid r egion so compl etelythat, though th e H enry Mountains form a prominentlandmark rising 6,000 f t above the plateau surface ,they w ere no t named an d describ ed until 1869 whenJohn Wesl ey Powell mad e th e first success ful trip byboat down the Colorado River. From th e beginningof w es tern explorations to th e pr ese nt day this areahas b een littl e visit ed , and trav elers still pass around it .Th e reasons ar e plain Trav el from th e west mnst crossth e rugged High Plat eau s a nd then s eek on e of the fewan d wid ely separat ed narrow canyons through thebarri er , nea rly 150 miles long , formed by th e hogbackridg es ( call ed r eefs locally ) of th e Waterpocket Fold,tl, e Capitol Re ef, and S an R afa el Swell . Th e 70mil es of barren d eser t , mo s t of which is cover ed by loosesand, extends from Mount Ell en to th e Book Cliffs anddiscourag es trav el from th e north. Th e canyons of theColorado Riv er and its tributari es all but prohibittravel from th e east and south. In addition , water isscarce . Only a littl e mor e than 5 in. of rain fallsannually on the plat eau so tlmt few s treams or springsmaintain th eir flow throu gh the annual droughtpcriod s .

P erh aps to mos t p eopl e the region offers few attraction s . I t is virtually a tr eeless plateau and broadar eas of bar e rock hav e no v egetation at all . Muchof th e s urfac e is cov ered with san d du n es that at manypla ces compl etely bury small valleys . Th e plateau isintri cately cu t by d eep canyon s who se walls can bedesce nded at very few plac es. Obviously such aninhospitable country can support only a small popula-


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4 GEOLOGY AND GEOGRAPHY OF TH E HENRY M OU N TAINS REGION, UTAH

FumR 1 . - in dcxDlo.pofUtah showlnJ!: th e location orthc Henry r.rOwltatns rcgion .


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INTR ODUC TION 5

ti on , an d no la rge se t tl em ent s were es tabli sh ed by th eIn dians or by th e whit e me n who follow ed . The ar eais use d prin cipally as ran ge lan d for stoc k gr azin gan d is includ ed in Ut a h Gr a zing Di st ri cts 5 an d 7.

In contra s t with th e surr o unding plat ea u t he th r eenor thernmo st H enry Moun t ains r eceiv e as m uch a s

18 in . of r ainfall annually ; perennial cr eeks an d s pri ngsar e num ero us; th e va lleys ar e V -sha p ed; t h e r id gesbetw een th e v all eys ar e rotmd ed ; and th eir slop essuppor t a mod era te fo rest. By comp aris on , t he twosou th ern mou ntain s ar e s mall an d arid , bu t th ey formon e of th e mo st rngge d sect ions of th e Colorado Pl a tea us.

PREVIOUS WORK

In 1869 in th e COln'se of hi s boat trip do wn t he Colorado Ri v er , John Wesley Pow ell n am e d th e H en ryMo untains in honor of P rofess or Jo seph H enr y , wellknow n ph y sicist , who wa s th en S ecretary of th e Smithsonian I nst itu t ion an d an acti ve s uppor te r of Pow ell 'sexp edition on the C olo ra do. Powell al so discove red a tthat ti m e th e m ou th of th e Di rt y D evil Ri ver.

Furth er in form a tion on th e ea rl y exploration of th eH en ry Mo un t ain s is give n hy Gilb er t as follow s:

* I< * J oh n F. Steward , a geo logist an d member of th e party[P owell' s] climbed th e cliff near th e mo u th of t he D irty D evi)R iv e r an d approach ed th e eastern base of th e mountains. H ereported that th e strata in th e mountain s ha d a q uaquaversaldip, ri s ing up on th e flanks from a ll sides.

T he fo llow ing year Pr of. A. H . T homp s on , * >I< >I


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' '''f ..- c, .'~ r '1'' ~ , ' "k ' ' ' '8-I ..:,. _ . ~ ' _ - ll _. ' ~ ,FlOUR!. 2.-Sk ctc he so fthc Henr y Mountain s reproduced from the field notebooks or o. K. Gnbert. A, View north ntong the cast s!de or Mount F.llen. Th e sto ck Is a t the south end of the high part of the moun

min, The mienl butto at tho left Is Ragged Mountain, a bysmalith. Juke s Du tte (B .11 Mountai n), another bysmalIth, is the butt e right of center . B, Vtcw west o f Mount Penn cll. Tho rtdgo marked"stn . 7" Is tho ITom mccollth; "511" Is the Dark Canyon laccolith. The Mount Pennoll stoc k forms the peak and extends south ward to Straight Creo k. which emerges from the mountain on tho north stde ofstation 71. Betwoon sta tions 71 and 164 Is Bulldog Ridge.

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INTRODUCTION 7

numb er of lin es. Poin ts refer red to in the no tes ar egive n numb ers on th e drn\vll gs so on e who know s thecountry hIlS no diffi culty und ersta ndin g ju st whichoutcrop s were vi sit ed .

Gilbert' s not es con tain numerous r eferences to precipit a t ion, t em pera ture, an d dir ec tion of the wind, an d

th ere were occo.sional references to timb er on th e mountains . F ew natural ph en om en a esca ped ob ser va t ion b yhim , tho ugh his obse rvations n atural ly d eal t primaril ywith geo logic feat u es. Hi s only whim sical recordin g isa sketc h of th e for e part of a pa ck mul e (fig. 3), entitled " Lazarus , Du k e of York " Th e h ead of t hemul e wa s reprodu ced in t he firs t edi tion of Gilb ert'sreport with th e c aption " ' Vays and M ea ns" .

Gilb e rt 's t rip to th e H enr y Mountain s was ma d e ata time wh en ma n y of th e western Indians st ill w ereho s t ile. Seven years earl ier some S lu V\vitz Indian s hadmurd er ed th e two Ho wla nd broth ers an d DUll n as th eytrav eled towards Kanab a ft er leaving Pow ell 's Col orad o

Riv er part y in th e low er part of Grand Ca n yon . Fi v eyears earli er th r ee members of Wl lCcier's pa r ty, wi t hwhom Gi lbert h ad wo rk ed , were amon g those kill edwhen Mohav e Apa che Indi ans a mb u sh ed the Ehren-burg-Wi ckenbtu 'g stage about 5 mil es wes t of Wi cken-

. - -.... '\.

j{,

}' IOUR 3.- Ways and l\reans, 187&-1947 (after O. K . Ollbert),

blU'g, Ariz.the lin es ofvember 1):

So on e ma y r elL d dee p thou gh ts b etweenGilb ert's no t es wh en he reco rd ed (N o-

' Ve find today a t r ail made by one 1iOrsC sho d or partly shod,othe r horses bare footed, barefooted mu les and barefooted colts,in all about 15 animals. Th ere i s 8 moccasin t r ack with them.They came down Cresccnt Creek, s t arted up the trail towa rdTrochu s But t e and stopped; one went ahead and turned b ackand then all went down Cresrent Cree k Canon . Af te r an inte rval th ey ret urned and went back up the c reek again. Th e coming tracks we re made ill we t sand , th e go ing in dry. Neit herhave been rained on . Th e tracks arc much scattered.

Our last st o rm was October 20. Fr o m all this we infer thata party of I ndi ans not fa m iliar \\ith the coun try came downCrescc nt Creek October 21 or 2 2 and afte r an int e rval of someda y s (loug enough t o go to the Co lorado and back) returned.They were less n um e rous than their (1 5) an im a ls. I t is notu nlike ly that they were Navajos who had st o lcn stock from astock ran ge an d were trying to cross the Colorado withoutpass ing through the se t tl ement.

An d again on Nov emb er 8:Ycste rda y we crosscd the Indian t r a il twice. Th ey ret urn ed

westwar d close to Hill oid Butt e [T ab le l\{ollntain) with 26 a nimals and at leas t 6 pai rs of moccasins. T hey passed eastw ardin two parties (one car Her than the o Uter ) crossing Cache Cree k[Sweetwate r Cree k] nea r the sout h twin [South Ca in evillc Mesa ).

F ew trai ls e xist eve n toda y in th e H enry Mountainsr eg ion bu t trav el h as been sufficien t to locate th e wa t erholes a nd t he least diffi cult and sa fes t routes for travel.Gilb er t had, how e ,' er , only th e dim trails of In di a ns andd eer to guid e him an d the ha zard s were co rr espondingly gre at . Hi s no t es sh ow t his. H e 'ro te, on Septe mb er 4:

On the m arch t he gra y mule Louisa r olls do wn hill wit h herpack a distance o f 50 or 75 feet. T he chief damage seems to be

a c ut and bruise on th e t.h igh and anothe r back of the car .On the 9tll:A chapter o f acc idents. Frank kick ed by Littl e N cphi in Ute

shin. Li gh t foot about played ou t and don.'1l twice. My packbuckcd off and th ree a lfogas torn. Evcning Epent in re pairs.Water in pock et s bad.

On th e 10th :W'c have to lea ve first thc h orse Lightfoot beh ind and then

the Ba ldfa cc mule . Th e latter is b rou gh t in thi s P . M. Th eho rse is to be sought in the morning.

SUcil in cid en ts appar en tl y becam e so co mmonpla cetha t no fu r th er mention wa s ma d e of th em un t il, onNovember 13 , he recor ded:

Panguicb rolled ovcr t.oday int o Cu rti s Cree k. T his is herthird ro ll ou the trip. Beck has accomp lished two and Gomas,J oe l, a nd Lou sey onc each. Our lit tle t.rain of 9 anima ls hasatta ined to se vcn [e ight?] rolling sc rape s.

C HRONOLOGY OF GILDER'r " s TR I P IN 187G

J uly to August 20: T ravel from Sal ina to R abbit Vall ey audexaminati on of the Wa te rp ocket Fold b y proceedi ng sout hward a lo llg it to ncar the s ite ofBak er r anch.


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8 GEOLOGY AND G E OGRAPHY OF TH E HENRY MOUNTAINS REGION, UT AH

Au gust 21: Trav e l around south edge of Swap M es a , acrossBullfrog Creek, an d pr es umably then up P ennell Creek an d alon g so ut h foot of MountHill ers to v icinity of ' Voo druff cabin.

22: Camp held.23 : Tr av e led to Mount E llswo rt h .2t: To Str a igh t Creek , pr ob ab l y near Coyote B cuC'hcs.

T r av e l via pass at head of Bl ac k CBuyon .25: U p Slat e Cree k, th en bac k up Coyote Bench es tocamp nea r Coyote Spring.

26 : C a mp he ld .27 : T o s ummit of Mo u n t Ell en, presumably ncar

sou th en d, an d ca mp a t a sp rin g su rround ed byfirs (probab ly in B romide B asin bu t possiblya t E lle n Spring).

28 : Camp he ld.29: Tra ve l d own D ugout an d Sw eetwate r C ree ks to

Cflmp near Frem o nt R ivE"r.30 : T o Fr e mont Ri ver between North an d South

Cain cville Mes as . C limb onto North Caine"me M es a.

31: Up F re mont Ri v er to camp by rive r ju s t belowCa p ito l R ee f.

September 1 to 10 : Travel to Gunni so n.

C H R O N O L O G Y O F G I U J E RT ' S T R D ' IN 1876

Au gu s t 30 : Star t by pack t rain from Gu nn ison, Utah . Gil-bert' s party consisted of himself, T ully, Averittan d Farnsworth (see p . 5) an d 9 anim al s forriding an d packing. For the first part of thetrip he wa s accompanied by D utton,Ma cC urdy, an d J.JCwis. Tr a ve l to Salinabrid ge.

3 1: Salina bridge to Ki n gs lVl ea dow.SeptemJx>r 1: Kin gs l\ l eadow to t he Wi dow's.

2: T he \Vid ow ' s to Fi sh Lake.3 : Fish Lake to N e phi Creek, in Rabbit Valley .4: Nephi Creek to Uppe r Co rral C r ee k .5: Camp h eld .6: Upper Co rr al Creek to ne a r T emple (P1easn nt )

Creek by th e Capitol fu ef.7: To lower T em p le (p l easant) Creek.8: Lower Pl easan t Creek to Bloo d y Hand s Ga p .Q: Bl oo d y Hand s Ga p to S\\eetwater Creek an d

aroun d th e north en d of St e phens M esa to th edr y wash next west o f Cedar Creek.

10 : D r y Ca m p to Cach e Camp, locat ed by Du g outCreek where it leaves Mount Ell en .

11: Climbe d Steele Bu t te . M o ved ca mp about 1}{mil es up Du gou t C reek.

12 : Du gou t C reek to Mo u nt Ellen, camp proba b lynear E llell Sprin g.

13 : Camp held. Examined North Summit Ridg e.14 ; Ell en Spring camp to lowe r en d of Sa'\\'lUill B as in,

probably by Bull Creek.15 an d 16 : Camp held. Examined roof of B ull C reek

la cco li th an d climbed J ukes Butt -e .17 : Bull C ree k cam p east to Granite Creek an d up

Granite Creek to head ot Butl er 'Wash.18 : Butl e r W as h camp he ld . C limbed high north

east point of Gr an i te Rid ges.19 : Bull e r W as h to th e sp ri ng on th e north s id e of

Copper Ridge.20: Copper Ri d ge to Slat e Creek , proba bly in th e

Sl at e C ree k dom e.

Septe mber 21 : Ca mp moVl ,(} to Box Spri ng, ill P enne llen P ass.22 : Camp held. C limbed th e H orn.23 : C limbed Ra gge d M o un t a in. Ca m p mo v ed to

wes t R d e of Da r k Canyon, a t base of MountP e nnell.

24: Ca m p he ld. C lim be d M ount P enne ll.25 : M oved to junclion of Bu lldo g an d St ra i gh t

Cree ks .26: M oved to South P ass, probab lY at head ofP enne ll Creek.

27 an d 28: Cam p he ld . Climb ed Stewart Rid ge to SummitUi d ge of Mo un t Hill er s au d climbed east ri mof M ine Canyon to th e peak of :\fo un t Hill ers.

29 : Sou th P as s to Cove Creek, p r o b a b l ~' above siteo f Sanfo rd ra nch.

30: T o T r achyte Cree k n ea r T r ac hy t e M esa.Oc to be r 1: Tr A.Chyte Creek to near s prinf:!S a t sit e of S ta r

r anch.2: Ca.mp held. Traveled to h ea d of Fourmile

Cree k an d r et ur n .3: M oved t o Bullfrog Cr ee k a few mile s above

Eg g nog.4: Ca m p held. C limbed po in ts of Em e ry sandstone

ov e rloo kin g \Vat.e rpocket Fo ld.5: M ov e up B ullfro g C reek to th e upper gorge

t hr ough th e Em e r y sa nd st o ne .6: Cam p held. C li mbed halfway li p ridg e on south

s id e of D ee r Creek, 011 west slo pe of Mo u ntP elllle li.

7 : Camp held. Climbed T arantula M esa, southrim.

8: Retu r ll to Ca m p 1, th e Cache Ca m p by Du goutCree k .

9: Ca che Ca mp to wes t s id e o f Ta ble Mountain.T wo pa cker s leav e for Rabbit Vall ey to ob -t a in additional su p p li C'S.

10: Camp he ld. Climbed T a ble M ounta in .) 1: IVTov e to creek with s prin gs, Ilorth of Ce d ar

Creek.12: Cam p held.13 : R etu rn to Cache Ca m p , by Dugout Creek.

14,15 , a nd 16: Camp he ld, wa iting fo r return of packers wh oarriv e on th e 16th.

17 : Move to Bu llf rog Creek, sout heas t of St e ph en sNarrows. Tr a ve l up South C r ee k an d southac r oss (o o t of South C reek Ridge.

18: Mo v e d own lhtllfro g C ree k an d cast a lo ng footof Emery sa ndstone sc a rp to P enne ll Cre ek.

19 : T o upper pa rt of Sill Canyon.20 : T o hea d of P enne ll C reek in South P as s .21 : Around south s id e o ( Mount Bill er s to \ Yood

ruff Spring, whe r e supplies we re ca c hed, a ndt hen to canyon draining no r thwest fr om

M ount Ellsworth.22 to 26 : Ca mp held. Climbed to summit of Mount

E llswo r th eac h d ay .27 : To Cache C ree k on northwest s id e of Mount

H ol lllC6.28 to 29: Ca m p held. Climbed no rt h slope of Mount

H olmcs.30: Move to sp rin gs near Star ranch.3] : T o Tr achyte Creek jus t be low head of canyon

in Navajo sandstone .


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}'H'lURE S.-Canyon views. A, Vlcw west aMOSS the Colorado River at the mouth of Scvenmile Canyon. Scale lndicatcc\ by boat In midstre:l.ID near center o( picture . n, View up Dirty nevll RI\-cr (rom the mouthor Hatch Canyon. Two small a lC()Yc arch

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FI(lURE It-Canyon views. A, Airplane vlcw northwest across the 00)ora(10 lUvcr at the mouth or 1'rnchyte Crook, fl typical canyon seeno. In the upper l e f t are the foothills of Mount ITlllors. Photograp h byNatlonnl Park Srrvicc. n, View D(M'thwostacross the Colorado River just Hbove Dandy Crossing. Indlnn ruins In right forcground, C , View down 011)n Canyon {rom the mouth of Sm ith Fork. T he gra"cltcrn)( .C is the CaHlornl'\ Da r. Jn, Navo.Jo sandstone; Jk , Kay enta formAtion; II". Wingate sandstone; Tr, Triassic formati ons; Pc, Culler torm'ltion (White Rim so.ndstone member o.n(\ top o( Orgo.n Rock tongue).

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FrOUllE 12.- View s alo ng the sou th eas t flank of the San Rafael S .... el l . A , Typical exposure of Shinarum p cong lomerate ( t hick capping lod gc) on "Moen kopi formation a mUe east of Boul der ('nnYlin. B , Clay beds inthe upper part of the Morrlson formation form badlands . View cast across the Muddy R iver a mile belo .... the R eef of the Snn Rafao l S .... ell. Goological Sur vey pack tmin in the va lley . C, View ..... est alongthe un con rorm ity betw('CIl the Morrison formation and the und erlyi ng S ummcn'llI e fonnati on . Oypsifcrous cong lomerate at the b a ~ cof the Morrison form ation fll1s channels eroded 50 ft into the e\ en! ybedded Summ crv!l1e fonnation. D , Thin beds of Carmel fonnation resti ng on massive Navajo SBndst()n e along the canyon or the Muddy River wh ere It c me r g c ~fr om the San Rafael Swe ll.

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STRATIGRAPHY OF TH E SEDIMENTARY ROCKS 73

the geodes were id entifi ed as goethite by W . T . Schallerof the G eological Surv ey.

Th e Curtis everywh ere g ra d es in to th e overlyingSummerville tlu'ough a transition zone 5 to 50 i t thi ckin whi ch gray sand ston e of the Curtis typ e alterna teswith brown fin er- grain ed sa ndston e an d shale of th e

Summerville type. Th e boundary is near the top of thetransition zone between the two formation s.No fossil s wer e found in th e Curtis in th e H enr y

Mountains region , althou gh in a field on so il-co veredCurti s near Notom a belemnit e was found b y a localres ident. Fossils of sp ecies common to th e S undan ceha v c been reported from th e Curtis in the northernpart of the San Rafael Swell.

Phy siograph ic expression. - A t most pla ces the Curtisform s smooth, gray slopes at the ba se of th e esc arpm en tform ed by th c Summ ervill e and MOtTison formation s.Th e slopes arc stee p and are covered by a very thinmantl e of tiny ro ck chip s an d fin er mat erial in part

litho sol deriv cd from the ov erlying Summerville.Locally the low est beds in the Curtis extend as a thinlayer capping broad b enc hcs of Entrada sandstone.

Mode of deposition. - Th e Curti s is interpreted as am arin e deposi t. Th e sout hea st shor e lill e of the seacrossed the H enry Mountain s r egion ; to th e north andwest it probably connected ,vith the exte nsive Jura ssicsea in northern Ut a h and Wyomin g.

SUMMBUVII,l ,}] FORMATJON

Lit hology and th ickness. - In gener al the Summervilleformation i s compo sed of well-bedded brown san dstonean d shal e an d t1,ins southward from about 250 ft at th e

north end of the region to about 40 ft in the valley ofHall s Creek (figs. 14 an d 15 ). But the formationth i cke ns an d thi ns irregular ly and ma y vary as mu chas 100 ft in a few miles.

Th e distinctive fea t ur es of the Summerville are it seven beddill g an d reddisll-browll color. Th e formationis compo sed of fine-grained reddish-bro\Vn sandstonean d sandy shal e in bed s 6 in. to 4 ft thick sepa rated bythin partings of red, green, and purpl e s hal e. Th esa ndy beds wea th er as sm ooth round ed flang es se parat edby para llel grooves alon g the shaly b eds. At somelocaliti es appreciab le qu an t it i es of coarser whit e andgr eenish-whit e sa nd stone ar e interbedded with thebrown sa nd stone, bu t are incon spicu ous b eca use theyar e covered by wash from th e browll beds. All th esandstone is fine-grained; so m e is c ros s-bedd ed on asmall sca le. Beds of gypsum o.re common in th enorth ern pa r t of the area but are absent to th e south.Undulatory b edding wa s sce n at Burro Wa sh , nearNotom, bu t probably this is du e to flowag e of thegypsum. Gypsum ve ins ar e ahundant eve n wh erether e are no gypsum beds.

Five miles sout h of Hank svill e a gypsiferous sect ionof Summ ervill e contains irreg ular ma sses of gypsum,som e seve ral f eet in diameter, distributed alon g beddingplan es. Most of this gy psum i s whit e, but som e isde licate pink . A 6-in. bed of brown lim estone ispr ese nt ill th e Summerv ille at Ba k er ra n ch. Local

ero sioll al unconformiti es or dia s tem s a rc present withintl , e formation at a few pla ces. No foss ils ha v e beenfound in th e formation.

Th e Sununerville formation i s unconformab ly ov erlain by th e Morri son formation. Channels in the topof th e Summerville filled with gypsum or cong lom erateof the Morrison arc numerou s, especially in the northpart of th e region . Som e of these channelt' arc 50 ftd eep. At some outcrops the unconformity i s angu laran d th e beds in the two formation s diverge by as muchas 5 0 (fig. 17). Alon g th e south s ide of tb e R eef of th e

Ftn u RR J7 .- U nooIlJ onnlty between th e Summerville lormnHon (Js ) D.nd overlying:Morrl so lJ fonnatlon (Jm ) at the south s ide of the P o iSon Spring Ben ches.

San Rafael Swell the Morri son locally cuts across 50 i tof Summerville beds in a mil e. In general , how ever,th e two formations appear to be stru ctura lly concordant .

Generally wbere t he b ase of t.he Morrison for ma tionconsists of coars e sa nd ston e, conglomerate, or gyps um,the contac t is recognized without difficulty, bu t inmuch of the region the basal Morrison b eds e10selyr esem bl e th e Summ ervill e an d th e contact is gradational.

Part of the irr egular thickening an d thinn ing of th eSumm erv ill e ma y be du e to inconsistency in pi ckingthe ba se of the formation in th e transition zone withthe Curtis. But mo st of th e irregularity probably isdue to eros ion of the upp er Summerville b eds befor.,deposi tion of the basal M o , , ~ s on .

Phy siograp hic expression. - In th e dese rt ,s tbe Summervill e formatio n crops ou t in a stee p escarpment oreIiff that is capped by resistant sandstone or cong lomerate belonging to the ba se of the Mon'ison formation(fig. 18B). Thi s escar pm ent is a p ersiste nt topographicfeature, both on th e east s id e of the reg ion wh ere thedip s arc low and on the north an d west si d es wh ere th eformation is tilted 15 0 to 30 0


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7 4 GE O LOGY Al.'VD GEOGRAPHY OF TH E HE)[HY MOUNTAlNS REG l ON , UTAH

FIGum : t S. - A, Coo] bed, about 6 fl thick, at th e to p or t he Ferron Slind';tone member of th e Mancos ~ h a l e. Over lying It Is th e Blue aate shale member. Vl.ewat } actor) tButte coa l mine. B. ClIns 8 1o l 1 ~Bullf rog Cr'('k nilfIr th e mouth O r c J a ~' Canyo n. J m, r..oforrison forTllation; I s, S um merville rOC Ill(ltlo n ; Je, Entrada sondSlone. Photo-graph by R. L. Miller. C, Stee le Butte. 'J ' hc Mesaverde formatl


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FIG ORE 20.-Vlews of the hogback ridge s. A, View of the Manco s shale northeast along thc CaillQ\'iIle Reef. Kme , Emery sandstone member; Kmbg, Blue OaUl sha le member; KInf, Ferron sa.odstone member; Kmt,

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Tununlr shale, members of th(l Manco s sha le. Photograph by George Orant, Department or the I nterior. n, EntraQa sanQstone "t the Roof of the Sail Rafael Swell. View east, about I mile cast of the Muddy River . CIJ...


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82

4 mi le sso u thw es t

of Ca in e ville

GEOLOGY AND GEOGRAPHY OF THE HENRY MOUNTAINS REGION, U TA H

3 mil esso u thw es t o f

Factory QUlle

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FIGURE 21.- Slratlgraphic sections showing le.t()l'81 cbanges In the l"crron sandstone member of :Manros sha le across the north end of th e llenry l\founta1ns region.


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ST R UC TURAL G E OLO GY AND FURM8 OF TH E I GN E OUS INTR U SION S 91

both th ey and th e la ccolith s ha v e th eir st eepest flankon t he s ide awa y from th e s tock.

Flow s tru c tur e \\ri.thin lh e intrusion s is ob sc ur e andon e is impr esse d mor e by th e random ori entation ofth e con stitu ent min eral s than b y th eir locall y dev elopedlin ear or planar arran gement. Alon g th e conta cts

th ere is consid erabl e slickensiding and lin ea tion ofcru shed min eral s (fig. 82 D ), bu t tlti s lin ea t ion generall yis in th e dir ec tion of maximwn dip of th e conta ctat th e parti cular locality an d conform s to irregulariti esof th e conta ct rath er th an to gener al tr end s. In th ein t erior of som e of th e la ccolith s can be found a crud epla ty s tru ctu r e th a t approxima te ly parall els the n ear es tconta c t and a crud e lin ear s tl'u ctur o approximatel yparall el to th e elon ga tion of th e lac colith. Shortfiss ur elik e s tr eak s of cru sh ed ph enocryst s ar e no tun CO mmon within th e in t ru sion s, bu t th ese also see mto b e local and irregular f eatur es , a s if reflec ting minoradju s tm en ts to mov em ents durin g or afte r fr eezin g.

'f h e intru sion s ar e well joint ed bu t mo st of th e jointsar e irr egular and seem to bear only casual relation to th econtac ts or sha p e of th e u1 t ru s tion . Colum ns ar e welldev elop ed locall y, part i cul"fl y wh ere th e intru sions ar ethin, bu t wh ere the intru s ions t hick en th e colum ns ar elost in an irre gular joint sys tem . Sh ee tin g pamll el toth e con t acts is even less c on sis tent aDd t end s to bein t errupt ed by sweepin g c ury ed joint s .

Th e s light m etamorphi sm throu ghout th e H enr y:Mountain s s ugges ts that th e intru sion s were n ot highl yheat ed and that th ey did no t yi eld mu ch volatil emat erial. Ev en above the th i ck lac colith s, s hal ebeds ar e m erel y indurated for a few f ee t . 'f h e mos t

int ense metamorphi sm is found in th e shatt er zon earound th e s to ck s hu t even h ere th e metamorphi sm ismark ed only b y con vers ion of th e shal e to hornf els,sl i ght induration of th e s and s ton e 1 and d e velopm ent ofepido te .

Th e fiv e mountain s ar e ve r y difl erent s tructurall y.Th e Mount El l en dom e is th e wid es t and h as a broadpla te aulil (e top wrinkl ed with man y small anticlinalfold s (pI. 8). Th e Mount Hill ers dom e is th e highes tand s teepes t (pI. 13) and th e anti clinal fold s over th elac colith s on i t and on th e Mount P enn ell dom e (1'1. 11 )lie m ostly on th e north and north eas t flanks of th edom es. 'r h e Moun t Holm es dom e is th e small est ( pI.16 ) an d i ts top is anti clinall y fold ed . N o subordinat eanticiul es ma r th e sy mm et ry of th e Mount Ell sworthdom e (pI. 16 ). ,Faultin g is res tl1ct ed to th e south erntw o mOUJILall s. 'l'h ese prin c ipal diff eren ces b e tw eenth e mowlwin s ar e illus tra te d b y t he s tru ct ur e contourma p (pI. 5 .)

I t is eas ily d emon s trat ed th a t th e small folds on th etop an d flanl( s of the big dom es wer e cau sed by theinj ec tion of th e la ccolith s, h ysmaliths , or oth er sa te lliti c

bodi es. Th e origin of th e big mountain dom es is lessclear but th ey app ear to b e du e to deformation th a ta ccompani ed ph ysical inj ec tion of th e s tock s (p. 148 ) .

Th e intru sive s tru c tu r es within th e mountains di spla ya grain ori ent ed UI two duec tions and approximatelyparallel to the two se ts of joints in th e s tru ctnral bas in

d espite th e fa ct that th e location of th e mO lll1tains see msto b ear no relation to th e regional s tru c tu r e.All of th e intru siv e ro ck is diori te porph y ry , except

som e monzoni te porphyry 011 l\10W1t P enn ell and som eve ry minor in tru s ion s of ba salt and aplit e. Th e difl erent intru sion s of diorit e porphyr y po ssess consid erabl etextul"ai VRliation bu t no cor r elation w as found b etwee n form of intru sion and te xtural vari e ty .

M O U N T E L L E N

Mount Ell en (pI. 7 , 8 ) is a s tru ctural dom e about5,000 f t. high and 15 mil es Ul diam ete r . No t only isth is dom e th e larg est, bu t it is mor e rec tan gular in outIUle and ha s mo re c renula tc d flank s than do th e dom esof th e oth er mountain s (pI. 5) . Th e major s tru c tu r e isop en to th e s outh an d m erges with th e s mall er : 'fountP enn ell dom e.

'r h e Moun t Ell en s to ck is locat ed in tb e Bromid eBa sin in th e . outh ern part of th e clu st er of in t ru sion sth at comp r ise tb e mOlmtain (pI. 9) . A doz en la ccolith sadja cen t t o or n ear th e s tock r adiate f rom it and probably were inj ec ted n early horizontall y from it .

Several intru sion s that are in part crosse uttu lg formNorth Summit Rid ge, which ext end s from Bull Cr eekPa ss to th e peak of Mount El l en. Th eir form i s no twell known but th ey seem to Ita ve been th e cent er of

mu ch of th e intru sive activity in th e north par t of th emountain and th ey are in t erpre te d as a par t of a ma s sthat wa s inj ecte d irr egularl y upward and outward fromth e s tock and that red tb e nortb ernmo st la ccolith s andrela t ed intru sion s.

Th r ee larg e bysmalith s- Tahl e Mountain (fi g. 40) ,Bull Moun t aul (fig. !O5), and Ra g ged Mountain (figs.27, 42A ) - ar e lo cat ed a t th e ou t er edges of th e clu ste rof la ccoliths on Mount Ell en.

MOUNT ELLEN STOCK

Th e "{ount Ell en s to ck is rou ghl y c ir cular in planan d is compo sed of mod erat ely homo geneou s porphyry .I t is s urround ed b y a shatt er zon e that con sis tsof a cOlnpl ex se rie s o f irr eg ular minor intru s ion s andse verely d eform ed sedim entar y ro cks. Bromid e Ba sin ,a wid e valle y at th e head of Cr esce nt Creek , hasbeen erod ed into th e s to ck. Th e s hatter zon e ha srem ain ed to form th e rim and oute r slop es oI th e ba sin(fig. 25).

Ero sion of th e Bromid e Basin ha s expo sed th e upper1,500 It of the s to ck. Th e expo sed sed im entary s trata


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Bromide Basin Factory B u t t ~I

Mount Ellen

FIGURE 27,-Ob li q ue \' icw northwest across Mount Ellen. The Mount E llen stock Is in th e Bromide Basin, whose rim is formed by the zone o f shattered rock s BroWld th e stock. Copper Rldge.is formed by th eaxtal bulge on the Copper Ridge laccolith, which also extends south under Garden Basin . The ridge Is allned with the stoc k. Also nlfnod with the SUlek Is the dlkellke ridg e on top of the Ragged Mountainbysmalith (foreground). PhOUlgraph by Fairchild Acrin l Surve)s.

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FIGURE 42.-Vlcws on Mount Ellen. A, Ragged Mountnin, lookJng n.cross the Canyon of Slate Creck. Noo.rly horimnt al beds of sandstone appear to pass under the mountain but they Brc turned vertica lly a t thecont1l.Ctwith the porphyry forming the upper half and core of the mountain. The Intrusion is a bysmalith. B, Vlowalong tho south side of the Ragged Mountain bysmalith showing sandstone bC!ds of the M orrisonformation dragged up stC->-

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S'I 'fm C 'r U RAL GEOLO GY Al\ TD F OR M S OF TIIE IG NE OUS IN T RUSION S 115

th ese dip s dimini sh pro gress ivel y awa y from th e intr u sion bu t a t th e south end of th e sy nclin e of theDakota san d s ton e the ro cks 300 to 500 ft from theconta ct , includin g th e Dakota , ' ' ' 'e ov erturn ed. Th eseov erturn ed s tr a ta lir e adja cent to th e n earl y horizontalb eds tbat rim th e can yon , so th e br eak betw een th edi p s is ex tr em ely sharp .

No roof rock s remain on t he bys malith bu t a s harpdi k elik e ri dge on t he c res t tr end s so uth eas t, is "lin edwith th e Moun t Ellen sto ck (fig. 27 ), an d probablyrefl ects an ori ginal intru s ive stt' uctu r e. I f so, th e (.opof Ra g ged Mount a in rou ghl y coin cides w itb th e original top of the in tf'Usion.

Th e alin em ent of thi s dikelik e s ummit rid ge w it h th eMount Ell en s tock fits th e radi al pattem of th e sat ellitic intru sions around th e s tock . Mo r eove r , a southea s tward , as well as an upward thru st , is indi ca t edb ecau se th e forma t ions un d erl yin g th e Coppe r Rid gela ccolith in Gard en Ba s in are s tructurall y about 300i t

high er than th e fOI'llation s so uth eas t of Ra ggedMountain. Pr esumabl y anoth er lac ,colitb 01 ' sh eetun d erli es th e Copp er Rid ge laccolith an d conn ect s theRa gge d Mountnin b ysmalith wi th th e Moun t Ell ens to ck. Th e s trati graphi c position of thi s inf en 'ed conn ec ting intru sion i s no t kuown o ut in th e vi c init ,y ofRa gge d Mountain it can be no hi gh er than th e Summ ervill e forma tion.

BURIED LACCOLITH S

Around th e foot of Mount Ell en ar c four an t ielinalfol ds th a t re se mbl e t h e an ticlin es OV er th e la ccoli t hsan d th ey undoubt eclly ov erli e buri ed la cco lith s. Th e sefold s ar e located on the cast , north east , an d north s idesof th e mo untain . No m etamorphi sm "" IS observe d onth ese fold s, bu t m e ta m orphi sm is slight eyeryv, here inth e H enl 'Y ~ l o u n t ai n s an d pa r t icul arly so wh ere th er eis con sid er a bl e s an d s ton e, as th ero is at u.ll Lut, on e ofth ese fold s. Two of th e fold s ar e c ut b y dik es thatt rend radi ally from the Moun t Ell en stoc k.

On th e eas t sid e of the moulltain, a t th e s outh , isth e Ma ze Arch which exposes th e entir e thi ckn ess ofth e Gl en Can yon group an d ha s mor e than 500 ft ofclosur e. Th e cast an d south east flank s o f this dom em erge with th e flank of th e la r ge Mount Ellen dom e(pI. 5). Th e dip s ar e s teepes t and th e displa cemen tby th e fold is g reat est on the s id e awa y from th e s tckan d a small dik e in th e dom e tr end s south east. Probabl y t h e dom e is und erla in by a la ccolith in th e Tria ss icor old er !'O cks.

Farth er north along th e eas t s ide of th e moun ta UI isth e Cr esce n t A" ch whi ch is cu t by " dik e that exte nd s1M mil es nor th east e rly. Th e southw es t flank of the!lIeh i s brok en by minor faults Pllrall el to th e dike(pI. 7) .

At R ese rvoir Basin , ca st of Jukes Butte , an anticlinal n ose plun ges north eastward (fig . 105 ) a::ld asimilar fold a t J e t Ba s in, north eas t of Tabl e Mountain ,plung es northward (pI. 5 ). Th ese two folds, like thean t iclinal no ses ove r th e lacc olith s, plun ge aw ay fromth e mo untain, bu t th ey diff er from th e Ma z e andCr esce n t Arche s in bein g op en towards the mountain.R ese rvoir Ba sin an


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STHUC. "TUHAL GEOLOGY A . t ~ DFORMS OF TH E IGNEOUS INTRUSIONS 117

Around th o s tock i s ' ' ' ' aurco le of epidotized indul'llt edrock. Thi s m e tamo'l,hi sm, even tluou gh slight , is n cver-thel ess morc in t ense than around th e k n m \ ~ lla cco lith s.Aplitic dik es and minor d eposits of sulfid e min eral sar e practically rest ri cted to th e s tock. Th e stru cturalpo s ition of th e stock at th e cen ter of a hug e sym m et" iea l

dom e and th e disco rdan ce between the s tock and sedim entary mck s turned up around it furth er distingui s hth i s intrusion from th e perip heral satelliti c one s .

In t he ce ntral part of th e st


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STRU CTURAL GEOLOGY AND FORM S OF T HE IGNEOUS INTRUSIONS 119

repr esent s one of the la t e intrusiv e phases. Probabl yther e was continued doming whil e tbese sills wer ebein g intrud ed . Their shap es s ugges t that the y wel'einj ect ed laterall y from th e dike s or o th er cro ssc uttin gbodie s, rather than from th e s tock , and tbat th eywere inje cted along th e s trike rath er than down the

dip of th e domed s trata .

DARK CANYON LACCOLITH

The Dark Ca n y on la ccolith form s a wid e and promin en t rid ge betw een :Mud an d Gibbons Sp .ings on th enorth side of J\Joun t P enn ell. Th e c reek in DarkCan y on i s in cised abou t 350 ft into the porph y ry of th ela ccolith bu t ha s no t ye t cut its wtty to th e floor. Th u sth i s c reek , lik e Bull Cr eck a nd Du go ut Cr eek on MountEl l en, did no t shift it s cours e off th e s tr u ct ur e durin gth e un cov erin g of the intnl sion.

Th e laccolith wa s probabl y inj ec ted slightl y eas t ofnorth from th e Moun t P enn ell s to ck (fig. 45) . I t is abroad flat-topp< 'u intru sion with a stee p nortll side an dless s t eep east and west sides. I t intl"ude s th e top ofth e Morri son f onnation , a t mo s t pla ces about 50 or 7 5ft below th e Dakota sa nds ton e, bu t lo call y alon g th esouth e a s t s id e i t {mt s up w ard to th e Dakota.

Soutll ells t of th e laccolith th e s tmttt ar e noorl y horizontal , but at th e edge of Lh e intru sion th ey are tmnedup ttbruptl y abou t 300 Th e y fla t t en again equall yabruptl y acro ss th e top of th e intru sion.

E as t of Dttrk Ca n y on th e roof is pr a ctioolly horizontal, but west of tb e can y on i t dip s about 15 0 W . FMther west th e dip incr eases t o about 30 0 and th e st eep

dip i s maintain ed in th e F e .ron sandston e in th evicini ty of Mu d Sprin g.

Tb e no .th eas t edg e of the la ccolith i s nearly s trai ghtan d th e adjoining Moni son bed s ar e turned up almo stvertically at th e contac t, Th ese s teepl y dippin g bed sabruptl y flat te ll and becom e n earl y horizontal onl y ashor t distanc e away from th e intru sion. Thi s is thedistal edg e of th e intru s ion and, in common with mo stot h er laccolith s in th ese mountain s, is s teeper and moreblun t than th e t wo s ides.

Wh ere th e trail cro sses Dark Can yon up s t .eam fromth e la ccolith , p01'phye y cu ts di scordantl y acro ss theDako ta san ds ton e 8Jld th e TUllllnk s1tale. From theup p er PM t of thi s di scordant ma ss a she et ext end snorthward a cross the F erron sanelstone and into th eov e rlyin g shal e alon g t he wes t flank of th e Dark Canyon la ccolith (fi g. 45).

THE HORN LACCOllTH AND ADIACENT INTRUSIONS

Th e Ho m lacc olith i s a lin ear bul ge of biotit e-b eMin gporphyr y th a t em erged northwMd from b eneath ash eet of diorit e porph yry . Th e axis of th e intru sion i s

alined with th e s tock; the general form is shown infigur e 45. No exposum s of th e floor wer e found bu tseveral exposure s of th e roof indicat e that the intm sionthin s east ward an d westward by a s tepping down ofth e roof. Th e la ccolith intrud es th e Blu e Gnt e shalen car th e top of th e Ferron sandston e bu t southward it

cut s downwat"d through th e sand s ton e, at leas t locally ,becau se s mall pa t ch es of F e .ron ov erli e it.

At th e high part of Th e Hom (fig . 46), call ed S enti-nel Butt e by GilbCl"t, th e la ccolith i s 1,000 ft or morethi ck. Vi ewed from a distan ce, th e upp er 100 ft ap p earsas a sh eet that is distin ct from th e low e . part of th eintru sion , bu t thi s ma y be onl y a w eathering ph enomenon con troll ed by the mor e ablmdan t joint s in theupp er part, becau se tb e ro ck in th e ri d ge is all on e ty peand close insp ec tion fail ed to reve al th e s ugges tedsbe eted s tmcture.

On th e cres t of th e ridg e onl y 2 to 5 ft of bak edBl u e Ga t e shal e se para tes Th e Horn la ccolith from th ehigh er shee t of diorit e pOl'phyry which occupi es mostof th e 2 sqnare mil es south of Th e Horn. Tlli s sh ee tis thin an d no t well expr essed topographi cally at th esouth end of Th e Horn bu t it t hicken s eastward and isbulg ed lin earl y . Southen s t of Th e Horn the bul geforms a ridg e on top of which ar e two nOl,thwardtr endin g dikelik e porphyry ridg es a bou t 50 ft high .The trou gh b etw een the ridg es is 1,000 ft lon g, 150 ftwid e, and contain s remnant s of th e roof of the BlueGa t e shal e. Th ese st ructure s a re aliu cd with tl, e s tock .

COYOTE CREEK tACCOIJTH AND NEIGHBORING INTRUSIONS ON THE EAST

SIDE OF MOUNT PENNELL

The Co y ote Cr eek laccolith cov ers about 1 sq mi bu tis no t very dis tinct lopograplli call y becau se it is sonearl y s unound ed by irregular small intrusions, Th olaccolith i s compo sed of diorit e porphyry that pl"Obablywas inj ecte d north eas tw8J'd from th e Mount P enn ellstock (fi g . 47) . I t is mod era l ely con cordant with th eenclo sing sedim ent.ar y ro cks nIthou gh n orth eas tward itcut s downward from basal Tununk to uppermostMorrison . Th e floo . is con cealed but th e roof i s wellro..l'osed b etw een the fork s of Co y ot e Cr eek whichar e inci sed about 300 f t into th e porpb y ry.

A sill of monzonit e porphyr y, abou t 75 ft thi ck , is

contained in th e s trata tum od up alon g th e s outh eas tedg e of th e la ceoli tho Several o th er s ills, composed ofdiorite porphyry, ar e h igher than the laccolith andextend con sider .bly farth el' north ruld south bu t th e ..s tructural relation to th e la ccolith i s no t known. Im -mediat ely abov e the la ccolith th e s ills ar e almo sthOl"izontal bu t n ea rer th e mountain they ar e v e .ticalas Me th e enclo sing s trata . I ass ume tbat m os t ofthem arc young el" than th e moun tain dome bu t that


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ST R UC T UR AL GE OLO GY AND FO RM S OF TH E IG NE OUS IN T R US IO N S 121

FIGURE 46.- Vl ew northwest a ~ T O S SPe n elJc n ! 'ass. The lI om isone of the lacco li tb::: Injected nort hward (ro m Mo unt Pennel l. Phoklgru ph by H. D. Mise r .

th eir dip s were in creased by ren ewed or continu eddomal uplif t.

Betw een th e Coyot e Cr eek and Dark Can yonlaccoli t hs is a broad sy nclin e th at contain s se veralsills who se agg regat e thi ckn ess is a pproximat ely equalt o th e Coyote Cr ee k la.cc oli t h. Th es e sills a re in tb e"ock s bel ow th e F err on sa ud st on e, so the sy nclinalst r uctu r e do es not app ear in fonnation s as high as theF erron .

M O U N T .fITI .L E l l S

Th e Mount Hill ers dome and t h e s t ock at th e ce nt erof it compri se the sou th ern half of th e mountain(p Is. 12 , 13) and pro vid e on e of the mos t spec tac ular

land scap e vie ws in th e H en" y :\10untain s ( figs. 50 , 108 ).To th e east, s outh , and w es t of t hi s part of th e moun ta inCr et aceous a nd upp ermost Ju rassic beds ri se gra d uall yo nt o th e bi g d OlTI e. :\1olln t n.illw nrd t.h e (lip s pr og r es -sively s t eepen a nd old er a nd old er formati ons, do wnt o t h e P ermi an, a re expo se d in color ful co n cent ri cba n ds. Th e res ist a n t a n d al mo st ve lt ical sa nds ton esfo rm hig h st ee p wa lls betwee n sk ike vall eys of th ebri ght ly color ed sh ales. T he co nt i n ui ty of th e for mati ons is brok en onl y by s ills a nd ra dia l dik es who se dar kmasses mottl e th e variega ted ban ds.

As on e goes t owa rd t.he cente r of ti, e dome an dappro ae hes t he s tock, t.he sedinl en t ar y ro cks becomemo r e and mor e cru shed and th e s ills and di kes becom em ore num ero us an d mu ch less regnlar in f orm. Adjoining t h e s to ck is a shatte r zon e in whi ch indiv idualin tr u sion s ar e t oo num ero us an d too ir r egular to b emapp ed separa te ly on a sca le of 1:3 1,680 and boun dar ies betw een th e sedinl ent my for m a t ion s " an b er ecog niz ed only in a ge nera l wa y. Th e width of thesh a t t er zon e r anges from hal f It mil e t o mor e tb an ! l

210 11 6 - 5 3 - - 9

mil e. In s id e th e s hatte r zon e is It huge ma ss ofmod era te ly homo gene ous d iOl'i te porph yry th a t comprises t he s to ck , about 2 )\ sq mi in area . Th e s tockan d its shat t er zon e ar e lo cate d som ewha t off th ecen t er of th e mountain dom e, and th ey di scordantl ycut ofr mor e than 2, 000 ft of st m t a he.twe eJ1 the southan d nor th sid es of the dom e.

La ccolith s on Mount Hill ers, as on Mount Pennell,ar e res tri cted to the north an d nortb east sides of themoun t ain . Lik e other lacc ol it hs in th e H enry Moun-tain s, howev er , t hey ar e to n g ue- hap ed , their arch edroof s fo rm a n t iclinal no ses that plun ge away from thes to ck , an d th e a xes of th e an ticlin es radiat e from th e

s to ck. Ev en th e porphyr y s h eet at Trach y te Me sa ,which is a bout 6 mil es frOln th e main mountain mass ,is elon ga te and ha s lin ear s t J'U otu r es alin ed with th es to ck. I t nppears to h e conn ecte d wi t h the main mountain ma ss by It flat-topp ed dilw or hori zontal plug . Th enear l y cir cular in t ru sions a t Bulldo g P eak (fi g. 48) an dBl a ck M esa probabl y a re bys m a li ths.

Plat e 14 show s t h e dis tr ibu ti on an d gen eral plan ofth e intru sion s on Mo un t Hill ers and th e posi tion of thecross sec tion s used in the diagrams illu s tratin g th e f orman d s tru ct ur e of the in t ru sions .

MO UN T HILLEBS STOCK

Th e Mount Hill ers stock, wh ich cov ers abou t 2}\ sqmi cent erin g in th e upp er par t of S ta r Ca n yon , form s arugge d ar e a, mantl ed with rock slid es, an d is a ccess ibl eonl y on foot an d even th en wit h d iffic ulty .

Gilb ert in te rp r eted th is in t rus ion to b e a lac colith butI believe it is a s to ck , b ecA1 use it cu ts dis cordantl y fromP e,mia Jl on the s outh to Upp er J ura ssic on th e nor th ;it is t he central in t ru sion of th e Moun t Hill ers cln s te r


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122 GEOLOGY AND GEOGR APHY OF TH E HENRY MO UN T AINS REGI ON, UTAH

"- ~ F . .

FIfl URE 47 .- Isomctrl c fence diagram of Coyote Creek lacco lith and neig hboring Intrusions on the ca.'!t sid e of Mount P Ctlllc ll. ' l' p, porphyr y; K mbg, Blue Gate sha le,member Kruf , Ferron san d stone m e m ~r . and Kmt, TUllunk s hale, members or the Man cos shale; Kd, Dakota sa ndston e; Jm, Mocr ison (orma tion ; Js , Summerv ill eformation and old er rocks.

an d th e other intru sions radiate from it ; th e metamorph i sm i s mor e inten se around it than around th e knownla ccoliths; epidote, albit e, an d quartz veins ar e mu chb ette r de v elop ed in an d around tbis central intru sionthan around th e known la ccolith s; and th e shatterzone around th e central intru sion i s no t dupl icatedaround th e known lacc olith s .

Th e st ock con sist s of mo d er a tely homog eneou s diorit eporphyr y of the type common in th e Henry ) ' lountain s.I t s main mass is centered in the mountain dome buton e lob e c ro ssc u ts into th e so ut h eas t flank of th e dom ean d a la r ge r lobe rr o sscuts into th e northwest flank .

Th e st ru ct u r e contour ma p (pI. 5) indi cates that th eHill e rs dome ha s about 5,000 ft of relief , bu t th i s is onl yth e minimum r eli ef ou t s id e of th e shatter zone , because

th e P ennian ro cks brou gh t up in their prop er s tratigraphic po siti on in th e shatter zone r equir e far mo r euplift than shown by th e st ru ct ur e contours on th eF elTon sand s to n e. Furth ermor e, th e south an d eastflanks of th e dome are in pa rt ver ti cal but th i s wa signored in order to proj ec t th e contours on th e Ferronagain st th e s ide of the s to ck.

South of th e stoc k th e sbatt er zon e is about half amil e wid e, an d on th e geologic ma p (pi. 12 ) th e ou t er

limit is drawn at th e base of the Chinle formation . Inth e ou te r pa r t of th e sha tt e r zone a t t be Woodruff mi n eth e entire Mo enkop i formation an d a few hundr ed feetof Pel1nian s tr a ta ar e expo sed, but th ese format ions m'eso s hatt er ed an d ir r eg ularly rut by minor intru s ion sthat no att empt was ma d e to ma p them se parately .In ge neral th e shatt er ed bed s dip about 55 away fromthe stock, but out sid e th e shatter zon e Up p er Tria ssicand Jw'a ss ic fonnations are v er ti cal . Th e dip s are l es sstee p half a mile from th e ou t er edg e of th e sha t te r zone.Th e sills an d radial dike s in t he s hatt er zon e an d in th ero cks turn ed up neaJ' by ar e composed of th e sarn eporphyry as is t b e stoc k, although seve ral texturalvari eti es are represented. Th ese minor intru s ion s dono t ex te nd so u th of th e belt of very s teep di p s.

On the w es t sid e of th e mountain th e shat t er zoneex tends n early a mil e through all th e s t eeply dippin gformation s to tbe less s te e ply d ipping ba se of th e Up p erCr e \;aceo u s. In this widened bel t of th e sha t te r zoneth e deforma t ion an d intru sive relations ar e complex ,bu t in crossing th e zone t he en t ire s tratigraphi c sect ioncan b e recogn ized in prop er se qu ence in th e float an d insm a ll expos ure s, Th e shattering, ther efor e, ha s not'h'agged th e formation s far out of position. Figure


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r : - ~: _ -H :..a,,--.a..-..-.....-. ....... ~ , ~

...

M ou nt Ell sworth

F I(;Ul1.E 4S.- 0bIlQUO view southeast a o r o ~s Mount Hillers. Mount HiUC'rs and the pointed peak to the right of It are In the stock . Bulldog P eak probably l


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124 GEOLOG Y AND GEOGRAPHY OF THE HENRY MO UN TAINS REGION, UTAH

108 is fl view acro ss some of Lh e formalio ns wh ere theysee m t o be cut off by U,is wes tward ext ension of th eshn l 1.t'r ZO ll e .

Th e Gl en Canyon grou p is c ut off a t th e e dg e of th estock in th e head of Sq uaw ClU'Yon. Fa rther northth e heds against th e s tock belon g in th e upp er part ofth e Ju r assic an d prob abl y ar e ba sal Morri son .

Th e shaLt er zone is mor e than a mile wid e in th efork s of Gold Cr eek , northea s t of the sto ck. Ncar th ecen ter of sec tion 34 , T. 33 S ., R. 11 E. , the fOllIlation ss tril( e nor t heast, but the s trik e c ha n ges throu gh efi st toso ut h eas t nea r the center of sec tion 35. In gener altht Se fOllIlation s ar e in their prop er s trati gr a ph icsequ ence although faulLing or irregular intru sionscn u se lninor r epet i tio n or ('uLLing o uL of so m e s trata .Th e older formu t ions are cu t off di sco rdantly along th enorth eust edge of the sto ck.

In th e shatter zone nOIth and north east of t ho

stock th e [arm a tion s dip l ess stee ply than on th e ot h ersides. P erhaps th e dips formerly wer e mu ch steeperthan now but when th e laccolith s were inj ecte d north-ward th e low er edges of the overlying, s tee ply dippingformation s ma y ha v e been drngg ed outwlUd an d up-ward by th e roof s of th e la ccolith s, th ere by wid enin gthe sha t ter zon e and r educing the dip s in it .

Mt Ellsworth

Th e east side of tb e s tock , be tw een Gold Creek an dGho st Creek , resembl es th e south sid e (fig. 49), butbetween Gho st Cr eek lUld Still C reek a lob e of the shat-ter zone exten d s so ut h eastward throu gh th e s teeplydippin g formation s ( fi g . 50 ).

SAWTOOTH RrnGE AND NORTB SAWTOOTH RIDGE LACCOLITBS

Sawtooth l\id ge, na m ed J ert y Butt e by Gilb er t , is2 mil es lon g, half a mil 0 wid e, an d 1,000 f t high. I tso ut h sid e is mostly a se ri es of cliffs an d rock slides;th e north sid e is less pr cc ipi tou s. Th e crest of th oridge is extre mely rou gh and ja gged, it s profil e givingth e ridg e it s nam e.

Two int erpr etat ion s may b e mad e of this intru sio nTh e expo sed porphYl Y ma y be th e bulging upper pnrtof a dik e, or th e porphyr y ma y be a rou ghl y horizontalan d more or less cylindri cal ma ss tr ending a littl e north

of eas t and ex tendin g to no great d epth. Whateverth e extent of th e intru s ion a t dept h it s upper part isdecidedly in eg ular. I t s to p consis t s of several por-phyry ridges, with the sedim en tary roof rocks stillpr eserved in some of the troughs betwe en them.Cataclastic lineation a t th e roof contact is usually inth e di r ec tion of maximum dip without r ega rd to th e

FIGURE 49.- VlCWSO Utll llcrOSS OoJc.l Crwk, showing th e sed imen t ar y formations turned steep l )' upward on the funk o(thc Mount UiJl Ol'S s lock . Some of th e ledges are sills.


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PInvilE .5O.-0bUque vlow north west across Mount BU1ers. The main mnss of ::\fount Hillers comprl!lOS the stoc k a.nd porlph('ra l sh:lttor zone. Around th is mounta in. (ormations toot range fro m Pcrminn toCretl\CCOus !lrC turnod up vertIcally agaInst tho sIde of the stoCk and shatter zone. Th!' conspicuous ltght-grny snndstoneIs Nllvu ]o. P hotogmph by Fairchild Aeria l Surveys,

;!

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~

'"~"~oc

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\ _ F o o t/FIGURE 51 .- l s o met r1c fenen dL.'\grom of the Sawtooth Ridge laccolith, the laooollth north o f Sawtooth Ridge, B hck :Mesa b y s m ~ U t hand Malden Creck lacoo Hth. Tp. porphyry; Kmt. Tununk sb.'"Ile,

momber of M ancos shale; Kd, Dnkotll sandstone; Jm, Morrison forml\tion: Is , Summerville [ormation: J e. Entrada sandstono; Jea., Carmel [ormation; In , Nilvillosandstono.

.....

~

"'"t""00'"

~tl

"'"0'"

'"

~'"

."

~~'"

'"'"

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0r.

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~en

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H

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STRUCTURAL GEOLOGY AN D FUHM" OF TH E IGNEOUS INTR US IO NS 127

ge nom l tr end of t he in t ru sion . At th e eastern end ofth e intrusion and at Trail Cre ek, Morri son s trataover lie th e porphyry , bu t at th e pea k th e ca ppin g ro ckis F err on sandstene. Evid ent l y t he cen t ral part ofth e porpbyry bulge d discord antly upwar d (fi g. 51).

On top of th e rid ge at it s east e nd is exposed a

concorda n t roof dipping so uth (fig . 52); a co ncordantfloor ma y und erlie the expos ed por ph yry. At th islocality the Morrison (lip s about 5 W., bu t th e sout hedge of th e porph yry cuts upw a rd abo ut 80 te highe ,s trata and for a di s tanc e of 20 f t from th o cont ac tth e ~ r o r r i s o nbeds al'C cons idera bly dragged an dcr ush ed.

Numerou s s ills, dik es, a nd oth er less reg ular apoph yses ex t end l ateral ly from the s teep s ides of th eintru s ion. A sill abou t 50 ft thic k, pr esumably connected with th e Sawtooth Ri d ge la ccolith (fig. 51) ,in t ru des the S mnm erville form ation and und erli esTh e Hoghack south east of Sawtoot h Rid ge .

At Saw tooth P ea k two porphyry rid ges e xt endsoutheast from the main ridge (p I. 12). On e exte n dsmor e Umn a mil e as a nano w dik e, tinnily en din g intwo oranche s, th e so u thern bran ch sh arpl y cur v ed.At mo st pla ces the contact s alon g tbis dik e are concea led , hu t n ea r the east end t he north wall dips abo ut65 NK

Wes t of Sawtoot h P eak a thin sill ov erli es th eD akota sa nd sto ne and a n irr egular dikelik e massextends a few hm ldred feel nor t hw este rly from th epeak. Thi s is the a nal og o f the dik es tr end ing sout h

east from the peak. Th ese dik es are ori ented a trig ht ang les to the nearby intru sion s and th ey are ano t ab le e xception t


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128 CEOLOGY AND GE OGRAPHY OF THE HENRY MO U NTADrS lU;C'; lON, UTAH

she et ma y connect it w it h Ulaek Nresa; th e two intrusion s ar e at about t.he same stratigraphic p osit ion.

Th e eas te m part of Lbe lacco lith north of Sawt oothRid ge is probably se parat ed from th e central an dea st e m pa r t of th e Sawtoo th Rid ge la.ccolith (fig . 5 1),becau se a lon g the east sid e of section 29 th e roof ofth

enorth

ern laccolith dip s southea s tward towal',l sSawtooth Rid ge.

BLACK MESA BY SMAIJTH

Bl ack Yresa is a n ea.rly circular hill havin g a smo o th ,gen tly s lopin g top and pr eci pi tous sid es about 600 fthigh (fig. 53 ) . Th e west an d northwe s t sides are dehriscovered, stee p slop es wher eas th e e a s t a nd southea s tsid es form a cliff , wi t h a talu s apron below.

Thi s intru sion r esemhl es Tflhl e Mountain , both ingeology and topographi c exp less ion . Gilb ert call ed i tth e Stew a.rd laccolith . Faultin g around th e si des, esp eciall y OIl th e eas t and sout h side s, is inf er red b) , anal

ogy wi th Tabl e Mountain. Th e conco rdan t 1'00f is abed of sandstone th a t belon gs in the lower p ar t of th e:Mol'llson fOl'Dlflt.ion . Th e fl oo r is no t expos ed.

Th e in tr us ion i s SUlTOundN l by 8 1.,1'0 La that. fir e nearl yhori zon ta l , bu t th ey ar e abruptly tu m ed up a few hun-dr od f ee t from th e porph y r y . Alon g tll( .>nor th enstsid e, forexamp le, about 700 ft from th e intru sion, t he Morrisonand Su nu n ervill e bed s dip gently west, b ut their dipbecome s abruptl y r ev ersed where t hey ri se onto theporphyr y, and about 200 ft from th e contact t he basa lrvlol'l'i son dip s 55 awn y from t he in trus ion . At seve ra lloca li t ies around tile north and nOlthw c .t sid es th e contact nnd , t mtlL adja cen t to it ar e almost verti cal.

although t .h e pOl1lhy ry a ppeal S to cut upward to slightlyhi gh er st rata . Th e st ructur e is e on ce nled along Lllrsouth and sout heast sid es.

'Wes t of the intru sion is a shalll syncl inal tro ugh f r om

Jukes Butte Morrison formation

whi cb the bnsa l MOI1'ison s trata ri se rath er s teepl y forabout 800 ft up th e flank and th ere flat te n aCro ss th eroof of th e intrusion . Prot .ludin g tl1.rough thi s flank andth e 1'001 ar e di k eli k e porphyry ridg es, th e mo st easte rl yof whi ch approximately mark s th e intru s ion 's highes tpoin t, wh ence th e sandston e roof dip s 5 to 10 in all

di r ectio ns toward th e sides.B eca use th e wid espread concordant roof ro ck is a b edof sa nd s to n e belong ing n ear th e base of the Morri sonf Olmation t he porphyr y mu s t re st on a floor of bas fllM orri son. How e ver , th e intrusion mu st cut di sco rd -antl y downward ncar its north eas t edge b eca use s t rataold er than tho se on t he roof ar e dr a gged upward alon gth a t edge (fi g. 51 ).

Th i s intrusion, more th an an y other in th e H enr yM ountains, a ppro ximates t he lacco lithi c structura l for mconc cive d by Gilb ert. But tbe intru sion probably WI I Sinj erte d la tera lly as a sat ellit e from the Mount Hill ersstock because, in co mmon with th e lacco liths and otber

bys malith s in the H enr y l\10Ul'ltain s, t he dikelik e rid gesin t he l'Oof aI'e alined with th e stock alld th e s tru c tu r e onth e distill side is s t,eepe r than on the s ide towanl thestoek.

MAIDEN CREEK LACCOLITH

Th e ;\J[ai dcn Cre ck lacco lith , actul1 11y liLlIe more thana sheet 50 to 75 ft thick, is expo sed at th e foot of Th eHogb . k cast of Bl a ck J"fesa ( fi g. 51 ). Gilb ert referr edto it as t.he D laccolith . Ex cep t for th e sCllrp alon g th eeast and north sid es t he intru sion i s no t di st in ct topogm phi call y, bu t thl' dark porph yr y contra s ts sha.rplywith the adjoinin g buff and light-r ed sa nd st one of th e

Entl'llds .Th e ol' iguml north edge of th e shee t was probabl y

not far f rom the pr esen t outcrops because th e ro o frocks ar e bent northward o ver th e porphyry nt. spvprn 1

FI GURE 53.-V lew ACTOSS Black Mesa on MOlln t TUllers. Dlnck l\{cSQ probably ill 11. byanoJith. It Is compo.


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l:)'l'UUCTUHAL GE OL O GY AND FORl\.IS OF TH E IGNEOU S lli'I' RU S IO N S 129

place s, as if to fonn th e s id e. Along th e east sca rp avert i cal di scorciolJlt sid e con tac t is e""posed locall y.P r esumabl y the intru s ion wa s inj ect ed from the dir ection of Sflwtoot h Rid ge and doe s no t extend und erBlack M esa, becaus e ill th e c reek dmining th e so u th eas ts id e of Black Me sa tb e roof of tb e :\;f aiden Creekla

ccolith dip s 20 toward t be m esa.TRACHYTE MISA LACCOLITH

Th e s hee t of porph y ry , about 100 ft thick, that isintrud ed into th e Entrada sa nd ston e at Tr a chyt e M esa

N

2000 Feet ro

FutURE M.- l SOtnc l ric fenee diagram of the Trachyte M esn M"O lIt.h. Tp. p()rphyry;Js, Summerville Crnmt.lon; Je, Enlrndn snn d sl.oncj Jea, Car mel (ormation; Jn,Nuvojo suudEt.oll e.

wa s na m ed th e How ell l acco lit.h by Gilb ert . Th e intrus ion , whi ch is about half a mil e wid e and mor e than I tmil e lon g (fig. 54), t rend s nortb eas lward and is ruinedwith th e Mount Hill ers s tock nIth ough th e lacco lith is6 or 7 mil es from th e s tock and topographically i solatedfrom th e mountain . Th e floor con tact of thi s intl"Usion

is ex posed at th e north east poin t of th e mesa and loca llyalong it s s outh east side. Th e roof contact and th earch o f th e roof ro cks are exposed at th e wes t edge(fig. 55).

Th e contacts o f th e la ccolith ar e mor e regular thanon e In ight anti cipat e in th e irr eg ulal' b eddin g o f them llSSive Entrada sflJlClstone. In fac t lh e floor contactis a lmo s t a plan e. Th e hi gh es t point of th e ex posedpm t of the floor i s neal' the ce.nter of the so uth east s ideof t h e me sa and from this poin t th e floor f a lls abo ut200 ft to th e nor th eas t point of th e m esa and a littlemo r e than 100 ft to th e so ut h emm o s t porph y ,"y exposu res. In gen era l the floor is about 100 ft l ower a long

tb e northwest than along th e southea s t edge of theintr usion . Th e hi gh es t point on the northw est edge isabout 600 ft wes t of th e t ip of t he mesa , and n ea rlystrn. ight n or t h of th e high point a lon g t h e south eas tedge . Th e ex posur es a re no t sufficient ly conti nuou s,bo w ev e . , to d e Lermin e wh e Lhel ' th es e diff nren ce s inaltitud e of the floor resul t from gen tl e dip s or from ase ries of s tru ctural st e ps in th e Roor.

On top of tI, e in trus ion is I t we ll-d evelop ed ",,, i es ofporphyry 'idg es and inte rven ing trou ghs, t he bottomsof whi ch contain r emnants of th e roof rocks . Th etrou ghs ar e flat-bottomed an d commo nl y 1000 ft longan d 50 f l or less in width (fig. 56). Some of th e ridges

ar e a1tnos t as wid e as tI, e trou ghs nnd ar e n.bout 15 fthi g h . S ump h av(' sharp cr es ts, ot h ers ar e bl'oadlyround ed . Th ese rid ges ancl trough s tr end north east-wllnl , pl1mllc1lo t he elongat ion of t.he lacc olith . They

FIG URE l)5.-VI(' w or ilt! norlh flank oCtile Trachylt) Mesa laccolith where t.he Entr ada snnd::to !lcfl ses on th" flunk and flattens 8.(!"OSS the rool or the laccolith.210110 - -53 - - - - ' 0


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130 GE OLOGY AND GEOGRAPHY OF TH E HE NRY MOUNTAINS REGION , UTAH

F m URE 66 .- Sk etch v lcw of rI dges i n l he roo f o r h e T rac h yte Mesa laoco mh . T he r id ges areoomposed o r )()I"phyry. Betwee n th em ate br ood fiat t rough s co nt ainingrem nants o f the roo f r ock s. Th e ri c4:es and lr oughs are psrn.l Je l t o t he e longatio n or t ile lacco lith . Sketc l lCd (ro m 8 phot ogra ph.

ar e n early s traight , though a few branch and th e mostea sterly one is sli ghtly curv ed (pI. 12).

Th e laccolitb apparentl.v thin s southw estwm d becauseits roof dip s a few d egrees off Lb e southw es t ed ge of th e""-posed porphyr y.

A mile up Black Canyon from Trachyte Me sa an dperfectly alined wilh th e la ccolith is a small ma ss ofporpb y ry wbich is ve r y s ugges tiv e of th e "d u ctolith"fOI1TI desc ribed by Grig gs (1939, p. 1l01). Th e porphyry, which i s expo sed in the north wall of the canyon ,ha s a concordant, nearl y hori zontal roof and di scordantnearly vertical side aga in s t whi ch th e Entrada sllJlds toneis dragged up steepl y. 'l'll e expo sed sid e is o bviou slythe so uth limit of th e intru s ion; th e intru sion cannotextend more than a few hundr ed fee t north because i tdo es no t appear on th e north side of the narrow rid ge.

Similar dikelik e ma sses o f porph yry alined with thisone are expo sed m ore full y northwe st of Bla ck M esa .Here th e porphyr y is demonstrabl y a nal1"()w intru sionlik e a dik e, bu t it cont ains man y wedg es of sedimentat yl'Oek (fi g. 57 ) and th e int.ru s ion ma y ext end to no g reatdepth. Lin eated catada s t ic stru c tu r e along th e conLu,c t g en erall y is n,lin ed 111 th e dir ec t.ion of ITI{D.1orrison formation.

ArOlllld th e eas t end of th e rid ge th e cont ac t at th ebase of th e porphyry is n o t well e"-posed . Di scordal l tstee p conta cts expo sed lo call y alon g th e so uth sid e


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Da ndy Crossin

FIOtiRli61.-0bUque view west across Mount Uolmes. Tbe mountain Is In the canyon part of the area and the Olen Canyon group o f sandstones that form the canyons rise onto Mount Ho lmes dome. Thointrusions are restricted 10 ~ h ecenttal part of t he dome and c o n ~ l s tor a small stock, some s mall lacooUths, and nume rous dikes and sills. The uplift at this mountaLn is less than at the oth er H enryMountai ns. Ph otOiTBph by Fairchlld Aerial Sur veys.

.

~g1

'o~

g$~-

~

~'dU

~'~'

I

ce


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136 GEO LO GY A ! ~D GE OGRAP HY OF 'l'HE HE N RY MOUNTAIN S HEG lO N , UT AH

F WURX62.- Vlew o rt he B u ck h o r n RldgcJacco lUJI (Tp. porp h yry) fr om Ihaesst. At th e left t he laccolit h i! abou l 200 t t thi ck and n ~ t : t011 tile C h inle ton nfilion {lie). At theright the Inl!co lith spli ts, a lower lo n gu e co n tillul n g lor a sho rl , d istance a long t he base ortha W ingate ssmlslonc (Jw) Rn d nil upper tong u e c ut ting ncross 300 It of Wln ggte

sandsto ne to Ih e top or h efor ma ti on.

Ske tcllfrolIla

phot ogr aph .

but nea,' the middl e of i ts south ern part , dik elik erid ges tr end 45 to Lh e axi s of Lhe nntiolin e ove r th ela c colith , A ven eer of th e C hinl e !'Oof is pr ese rvedon ea ch s ide of the di kes.

Th r ee of th e four quach'an ts betw een Il, e int.ru s ionsju s t d esc ribed ar e a ppro"imat el,v bisect e d hy o th ersatelliti c intru sions, B etw een Bu ckhorn Rid ge andW es t Spur several dik es, s ill s, and v ery smallla ccoli t,hstrend roughly nor thw es t, about parallel to a fault thatbr eak s th e nOl-thwes t flank of th e mountain dome,On the wes t s ide o f Cac h e C reck a la ccolith , about.

100 ft thi ck, ext end s abou t 1,500 ft fr om th e s to ck ,thin s nor thward , a nd c ut s upwarrl tJu' ough th e low e)' 200ft of the Wingat e (fig, 63) , A few hundr ed fee t ( ~,' : t ] ] e r

"

_: ... : ''1


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STRUCTU RAL GEOLOGY AND FOnM S OF THE ICKEOUS INTIlL"SIONS 137

tilt ed to almost cvc l'y position , but dip chi efl y awayfrom th e mountain . Th e deformation ends westwal'dalong a nOl'mal faull and il ends northw ard alonganothc l' fault whi ch is at the foot of Sout h Spur. East-ward and south eastw a.l'd th e deformation b ecome sprogressively less. Along tJ,C soutJl\ve s t side of tJ, edefol'med al'ea is a I'everse fa ult alon g wllich th eKayenta ha s been t hr u st southwa l'd over Navajosandstone. Th

usgs pp228 henry mtns geo geography

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