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BULL. GEOL. SOC. AM. VOL. 18, 1906, PL. 24

GENERAL MAP OF NORTHEASTERN UTAH FROM WASATCH MOUNTAINS TO GREEN RIVER Showing location of areas discussed Downloaded from gsabulletin.gsapubs.org on July 31, 2015

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA Vol. pp. 287-302, PL. 24 JULY 13, 1907

UINTA MOUNTAINS*

BY SAMUEL FRANKLIN EMMONS

(Bead before the Society December 29, 1906)

CONTENTS Page Introduction ...... 287 Topography of the region...... 287 Purpose of the paper...... 288 State of geological know ledge...... 289 Methods of work...... 2&0 Major Powell’s investigations...... 292 Recent investigations ...... 293 Geology of the region...... 295 Structure ...... 299 Correlation ...... 300 Origin of Green river...... 301

I ntroduction

The Uinta mountains form one of the most interesting and unique ranges in the Cordilleran system, in that they have a typical anticlinal structure with east-west axis and show no evidence of igneous action con nected with their uplift. In them are exposed, moreover, the only Paleozoic outcrops arising above the covering of Tertiary sediments in the upper part of the Colo rado Plateau region, which thus furnish the sole connecting link between the Wasatch uplift on the west and that of the Rocky mountains on the east.

T o p o g r a p h y o f t h e R e g io n

Topographically, they form a rather flat elliptical dome about 150 miles in length along their main axis and 20 to 25 miles in average

•For the general location map (plate 24), showing the geographical position of the area discussed, I am indebted to Professor C. P. Berkey, who used it in his paper, “The Stratigraphy of the Uinta Mountains.” Bull. Geol. Soc. Am., vol. 16, 1904, plate 89. Manuscript received by the Secretary of the Society May 20, 1907. XXV— B ull. Geol. Soc. Am., Vol. 18, 1906 (287) Downloaded from gsabulletin.gsapubs.org on July 31, 2015

2 8 8 S. F. EMMONS----UINTA MOUNTAINS width. The interior of the ellipse has a general level of about 10,000 feet, out of which rise sharp, narrow ridges and peaks of horizontally bedded quartzites to elevations of 12,000 and 13,000 feet. The plateau like surface between the peaks consists of a series of shallow, glacial basins, well clothed with pine forest and studded with innumerable glacial tarns. The streams that drain these basins run in a series of rapidly deepening canyons with nearly vertical walls that reach depths of 3,000 to 4,000 feet before they emerge into the open plain country on either flank. On the broad, flat spurs between these canyons gently sloping Tertiary beds lap over the upturned Mesozoic and Paleozoic to elevations attaining in some places 10,000 feet, which, together with the abundant accumulations of moraine material, effectually mask much of the under geology, especially on the northern flank. This general description ap plies more particularly to the western two-thirds of the range. Toward the eastern end the general elevation of the interior decreases, the higher peaks reaching elevations of only 8,000 to 9,000 feet, while the mountain mass widens very considerably and the structure becomes correspondingly complicated. The single anticlinal fold becomes double, while at the eastern extremity, before the older rocks disappear entirely under the Tertiary beds, the axes of folding take a more north and south direction and the uplift ends in two isolated anticlinal billows that raise their crest a little above the sea of horizontal Tertiary beds that now surrounds, but once covered, a great part of the present mountain mass. The central core of this mountain mass consists of a series of quartzite beds, over 12,000 feet in thickness, whose age has long been in doubt. On three published geological maps they have been assigned successively to as many different periods—on the Fortieth Parallel maps to the Car boniferous, on the Powell map to the Devonian, and on the Hayden maps to the Silurian—whereas in point of fact they do not belong to any one of the three.

P u r p o s e o p t h e P a p e r

A generation has passed away since these maps were made, during which time the advance in geological knowledge of the West has been so great and the change in methods of work so radical that it is difficult for the younger generation of geologists to appreciate the conditions under which geological work was then done. It is my purpose in this article to explain first how it came about that such conflicting statements were made, incidentally pointing out the difference in conditions and methods of work between that time and the present day, and finally, as a result of a reconnaissance during the past summer, to give my conclusions as to Downloaded from gsabulletin.gsapubs.org on July 31, 2015

REVIEW OF RESULTS OF INVESTIGATIONS 289 the age of the quartzite series and of the Paleozoic beds which overlie them.

S t a t e o f g e o l o g ic a l K n o w l e d g e

The only systematic exploration of the entire range was made by the Fortieth Parallel party under my charge, in the summers of 1869 and 1871. In the same years Powell made his famous explorations of the canyons of the Colorado, and in so doing traversed the eastern end of the range in his boat journeys down the meandering canyons of the Green river. In the summer of 1871 Hayden made a hasty reconnaissance along the northern slopes of the range, penetrating the central core at a single point near the head of Blacks fork, where he found Carboniferous fossils in the flanking limestones and “suspected” that the underlying quartzites might be Silurian from their resemblance to the Potsdam sandstones. During the seasons of 1874 and 1875 Powell headed parties that studied the geology of the eastern part of the range and the surrounding Cre taceous and Tertiary regions. From that time until 1903 there is no record of any geological study of the range. At the time when the Fortieth Parallel field work was being carried on, what was known of the geology of the Cordilleran region was mainly derived from observations of geologists accompanying military expedi tions, generally as surgeons. It may be summed up as follows: On the Great plains, especially about the upper Missouri river, Meek and Hayden had established the Cretaceous section and named its five divisions, but were uncertain whether the upper coal-bearing member might not more properly be classed as Tertiary. The beds beneath them were recognized as Jurassic from their fossils, while the red sandstones under these were judged from their position and lithological character istics to be probably Triassic. Unconformably over the whole lapped various series of fresh-water Tertiary beds, whose age was not yet deter mined, though in the very summer in which the Uinta work was being carried on the first vertebrate remains were being collected from the Eocene beds of the adjoining Green Eiver basin. In California the auriferous slates had recently been determined to be of Jurassic age, which was specially interesting as affording a decided negative to Murchison’s hitherto generally received dictum, that gold only occurs in rocks as old as the Silurian. From the wide mountain region between the Sierra Nevada and the Eocky mountains, popularly known as the Great American desert, Car boniferous fossils had been brought back by the various government Downloaded from gsabulletin.gsapubs.org on July 31, 2015

290 S. F. EMMONS----UINTA MOUNTAINS expeditions that had penetrated it; but beyond this nothing was known of its geological column.

M e t h o d s o f W o r k

The work of the Fortieth Parallel geologists, it must first be noted, did not claim to be a survey, but was explicitly called an exploration. It was carried on in regions that not only had never been mapped, but of which the topography, except in its very broadest features, was entirely unknown. Each working party consisted of a geologist, a topographer, and a barometer-carrier, with the necessary camp men and military escort. The necessities of topographic work required the occupation of every peak in a mountain range; hence the location of the successive camps was made rather with reference to the possibility of reaching such peaks than because they were the best points from which to study the geology of the surrounding country. In regions like the Uinta mountains, diffi cult of access and remote from any lines of communication, any revisit ing after the completion of field work was quite impracticable. So large were the areas laid out for the field work of each season that the utmost speed was necessary in order to go over the whole ground be fore snow rendered geological work impracticable. Thus the Green Eiver sheet, which covers an area of over 15,000 square miles, including the greater part of the Uinta mountains, was completed during the single field season of 1871, and for the study of the Uinta mountains during the two seasons of 1869 and 1871 less than three months could be given to actual field work, no small part of which the geologist in charge of the party had to devote to tasks not strictly geological. The general system of work was to construct in our minds, from field observations, a tentative set of geological divisions, based primarily on lithologic distinctions, and, from each successive peak visited, to work out the structure of the surrounding country as indicated by the lines of outcrop exposed. As we had no maps, we used only breast-pocket note books in which to record our observations; hence the ideas we formed as to the geological structure of the country visited could not be fully put on paper until the topographer’s notes for the whole area surveyed had been platted and engraved, and our tentative geological columns modified or confirmed by the determination of our fossil collections by specialists. Owing to a peculiar combination of circumstances, over two years had elapsed after the final completion of our seven years of field work before all this was accomplished. Downloaded from gsabulletin.gsapubs.org on July 31, 2015

METHODS OF WORK 291

In the case of the Uintas, lithologic distinctions in the Mesozoic and more recent beds were sufficiently persistent to permit a ready tracing of the structure, especially in the eastern part of the range, where the anti clinal arch is lower and has been more completely denuded of its Tertiary covering. This is not the case, however, with the Paleozoic beds; for, although the west end of the range, which we first visited, is separated from the Wasatch by a covered gap only 10 or 15 miles in width, it is practically impossible to trace there the lithologic succession of beds below the Weber quartzite observed in our key-section in the latter range. Our first visit to the Uintas, at the close of the field season of 1869, was curtailed by shortness of provisions, due to the forced abandonment of our wagon soon after leaving Provo valley, and when we finally reached the valley of the Duchesne, which was the eastern limit of that season’s work, it was found impossible to ascend the canyon above the forks be cause of beaver ponds, which were impassable to our animals. We were therefore obliged to abandon its exploration and climbed Rhodes spur, on its western side, in order to reach the summit of the range at Bald moun tain, from which we shaped our course westward again. The field work of 1871 was carried on from Port Bridger, on the Tertiary plains to the north of the Uintas, as a supply camp, from which two trips were made across the range to its southern flanks; but the necessities of the work did not justify going so far west again as the main Duchesne river, and thus a considerable gap was left between the two seasons’ field work at the very point where the best and most contin uous Paleozoic exposures are to be found. When, in the winter of 1874—1875, the working up of our material was so far advanced that we could draw in the geological outlines on the Green River sheet, there was a question as to what color should be given to the great quartzite core of the Uintas. Its estimated thickness amounts to about 12,000 feet. Above it is an uncertain thickness of beds, largely limestones, with some siliceous members, the fossils collected from which were determined by the paleontologists to be decidedly Upper Carboniferous, and for the most part rather high in that forma tion. In his one trip into the interior of the range, when he had climbed mount Agassiz at the head of Bear river, Mr King had collected from the talus slopes of that peak a well preserved Upper Carboniferous Productus in Uinta quartzite. In the typical Wasatch section, as shown in Weber canyon, there are 5,000 feet of Carboniferous quartzites, with 2,000 to 2,500 feet of cal careous and argillaceous Carboniferous beds above them, and about 9,000 feet, mostly limestones of Carboniferous, Devonian, and Silurian age, Downloaded from gsabulletin.gsapubs.org on July 31, 2015

2 9 2 S. F. EMMONS----UINTA MOUNTAINS between them and the Cambrian. Below the latter, in other parts of the range, a still larger body of quartzite is found, having a thickness of at least 12,000 feet. To one or the other of these quartzites it was evident the Uinta quartzite must correspond. Its lithological constitution re sembled the latter more than the former, though the resemblance was not very close and as a factor of correlation it was not considered of prime importance. To correlate it with this formation involved the assumption of an unconformity as the only way of accounting for the disappearance of the Devonian and Silurian formations of the Wasatch section, which were evidently unrepresented. No such unconformity had been observed, however, and one of the rules laid down by Mr King for geological mapping was not to represent any such features as faults or unconformities which were not proved by actual evidence in the field. Hence, with some misgivings, but as the only alternative, the doubtful quartzite was correlated with the Weber, and so mapped. That such an unconformity had actually been observed by Major Powell in the deep canyons of Green river, which we had been unable to explore through want of boats, was only known to us some years later, for the following reason:

M a jo r P o w e l l ' s I nvestigations

At the close of the field season of 1871 Major Powell paid me the com pliment of asking me to explain to him my ideas of the Uinta structure, saying that his observations in his boat journeys down the Colorado, being necessarily confined to the immediate vicinity of the river, were difficult to coordinate, and he felt it would be of great help to him in working them out to thoroughly understand the Uinta uplift, which was evidently the key to the whole section. At that time he did not mention the unconformity by erosion, nor was the question of the origin of Green river discussed; but in other respects we compared notes freely and agreed in all essential points. When, a few years later, after he had borrowed a proof-sheet of our topography of that region, it was learned that he proposed to publish a volume on the Uinta mountains in the near future, it was realized that he would probably secure a priority of publication over us, since, though the part of my manuscript relating to the Uintas was already written, it must necessarily wait until the report of the entire Fortieth Parallel region was completed before it could be published. In a vain attempt to obviate this, Mr King, on November 15, 1875, caused 12 printed copies of the geologically colored Green Eiver basin Downloaded from gsabulletin.gsapubs.org on July 31, 2015

m a j o r p o w e l l ' s I nvestigations 293 map, signed and dated in his own handwriting, to be distributed to as many of the leading geologists of the country. When the Powell report appeared (without any reference to our pre vious studies) the most important difference between his determinations and mine was as to the age of the Uinta quartzites, which he tentatively assigned to the Devonian, having found an unconformity by erosion between them and the overlying Carboniferous. As Whirlpool canyon, in which the unconformity was seen, was in a region of very complicated faulting and folding, Mr King thought it possible he might have been misled in his observations by the effect of perspective in observing faulted outcrops. It was, however, impossible at that late date to verify this fact, but we were certain that a quartzite series of that thickness could not be Devonian. A foot-note was therefore inserted in our report,* stating that if such unconformity exists, the quartzite series, which we had called “Weber,” must represent rather the great quartzite formation underlying the Cambrian of the Wasatch. My later geological work in the West has confirmed this conclusion, as I stated in my article “Oro graphic movements in the Rocky mountains.” f

R e c e n t I nvestigations

It still remained, however, to determine what part of the Wasatch sec tion is represented in the western Uintas, whether the unconformity can be detected there, and what is the true correlation between the formations there represented and the Grand Canyon section, on which Powell had based his divisions. I had hoped that long ere this these questions would have been finally settled by an areal survey of the region, made by geolo gists of the U. S. Geological Survey, and have hence deferred any further reference to them. In the summer of 1903, at my suggestion, Mr J. M. Boutwell made a reconnaissance examination of the iron ore deposits on •Rhodes spur, in the course of which he obtained an undoubted Mississip- pian fauna from the limestones J overlying the great quartzite series, thus definitely proving that the latter could not be Weber. During the same summer Mr Charles P. Berkey had an opportunity of studying in considerable detail the geology of the region around the Duchesne river, and discovered a considerable thickness of shaly beds beneath the limestones and separated by a fault from the Uinta quartz ites, neither of which had been noted by me. He also claimed to have found two unconformities by erosion in the Paleozoic series, and on the

* Descriptive Geology, vol. ii, p. 199. f This Bulletin, vol. 1, 1879, p. 256. t U. S. Geological Survey Bulletin no. 225, p. 225. 294

LAMOTTE PK MT. AGASSIZ DUCHESNE RIVER BLACKTAIL MT. Downloaded from Thi letn vl 1, . 517. p. 16, vol. tin, ulle B is h T * U Uj lUj K j ' f w m o CO ^ UJ q: mhy § < o < J ■ _J UJ < J < Q x «1 J > cr z CO* u . . MOS I A MOUNTAINS TA UIN EMMONS— F. S. gsabulletin.gsapubs.org westward, to empty into Salt lake, while the latter latter the while lake, Salt into empty to westward, cliffs. The canyon widens out quite suddenly in in suddenly quite vertical out widens nearly canyon The by bounded cliffs. canyon, practically narrow, impassable a in flows it which quartz- through Uinta the ites, bedded in are horizontally almost course Duchesne’s and even The the of miles bends 12 river. Colorado then first or Green and the miles, join 30 to to eastward 25 for then south courses northward, flowing two of first crest the northern range, the west the near the Agassiz, at mount plateau of of base bit same the on source their at his. somewhat with are variance conclusions my hence and points, I though work, Berkey’s Mr of acumen and gence years. many for undertaken be not may that presenta immediate for accuracy sufficient with to me enabled has data' Weeks, Mr by general by furnished supplemented kindly obtained, thus tion continues to form an imposing gorge 2,500 to 4,000 to 2,500 gorge imposing an form to continues range, entire the in section continuous most visited not the it, of east Duchesne the to the region examine the to and valley enabled was I posures, cir entire the making was who Weeks, B. F. Mr of tively.* have to him discrepancies by assumed views the relative reconcile the between should which column the shales beyond the Iron Creek fault, but still still but fault, Creek Iron the beyond shales the important some on him with differ to forced am survey areal detailed a await final still whose must questions many solution are there though structure tion, Uinta of features general the determine informa The canyons. River Green the outside contains happens, it as which, work, original my in ex Paleozoic its of study a in range the of cuit respec myself and Powell by maintained been basis of these new facts constructed a geological geological a constructed facts new these of basis The Bear, Weber, and Duchesne rivers all have have all rivers Duchesne and Weber, Bear, The y bevtos er etmn t te intelli the to testimony bear observations My During the past summer, through the courtesy courtesy the through summer, past the During onJuly31,2015 Downloaded from gsabulletin.gsapubs.org on July 31, 2015

r e c e n t investigations 295 feet below the flat-topped spurs on either side. About 8 miles below the Iron fault, near the site of the proposed town of Stockmore, the so- called West fork comes in from the west after running for 25 miles along the strike in the red beds of the Permian or Trias. Below the forks, in the softer Mesozoic rocks, the valley becomes still wider and contains considerable bottom land, while the bounding ridges have worn down into low hogbacks, except where protected by a covering of Tertiary beds, lapping up on the spurs or occasionally standing out as residual mesas, like Blacktail mountain in the section (figure 1). The magnificent section of Paleozoic beds exposed along the walls of the gorge is rendered rather difficult to read, through the abundant slips or faults parallel to the stream, by which narrow slices of the walls are let down a few hundred feet here and there, probably by sapping, so that portions of the cliff sections are duplicated. This may account for Mr Berkey’s tendency to overestimate the thickness of his various divisions of the Paleozoic rocks. Another peculiarity of topographic structure is observable at the head of the side ravines tributary to the main valley when they occur in lime stone formations. In the midst of a remarkably well watered region, these ravines have no running water, and in their basin-like heads are many minor depressions without outlet, such as are characteristic of moraine ridges, but in shape rather longitudinal than round. On either side of the main valley, near the mouth of the ravine where these were first observed, there are large springs issuing from the base of the cliffs, in streams 15 to 20 feet wide, with sufficient volume of water to supply irrigation ditches which extend to the arable lands many miles down the valley. Hence the explanation that suggested itself was that, in the easily soluble limestones, surface waters had eaten their way along cracks and small faults, finding their run-ofl in such springs, and had thus eroded increasingly large caves that had finally collapsed, producing something analogous to the sink-holes of the western Appalachian region. This hypothesis was later confirmed by the finding of a typical Kentucky sink-hole with circular limestone walls and a funnel-shaped bottom. The structure is developed on so large a scale in this region that it de serves a special name, for which sink-hole or karst topography is sug gested.

Geology op t h e R egion The geology of the region is not so easy to read as at first glance would appear, because the cliff sections along the valley are complicated by the slips or faults mentioned above, and on the flat-topped spurs, owing to Downloaded from gsabulletin.gsapubs.org on July 31, 2015

296 S. F. EMMONS----UINTA MOUNTAINS the generally low angle at which the beds stand and the peculiar topo graphic forms, the true succession of the respective exposures is often

sMiles Contour interval 100 feet.

W Z à WEBER QUARTZlTE WASATCH LIMESTONE OGDEN QUARTZlTE SHALE SERIES UiNTA QUARTZlTE

F ig u r e 2 Geological Sketch Map of Duchesne Canyon Region, Western Uinta Mountains. difficult to determine. The lithologie constitution of the beds has suf fered a remarkable change from the Wasatch section, considering the short distance that separates them. Downloaded from gsabulletin.gsapubs.org on July 31, 2015

GEOLOGY OP THE REGION 297

The Wasatch limestone has shrunk to about 1,000 feet of buff, cherty, calcareous beds, alternating in the upper part with white sandstones. Although the limestones are always light colored, they often present a red or striped appearance in cliff exposures, and thus resemble rocks of the same horizon in the Grand canyon of the Colorado, where they are stained by waters seeping down over their face from red shales above, and were hence called by Powell the Eed Wall limestones. They carry Pennsyl vanian fossils in the upper part, and Mississippian in the lower. Beneath these are quartzites with interbedded conglomerates and sandy shales, generally white or greenish, often red by oxidation, which are in extremely variable thickness, reaching a maximum in the Duchesne val ley of 1,100 feet. Mr Berkey’s surmise that these correspond to the Ogden quartzite (now considered Ordovician), though as yet unsupported by paleontologic evidence, is considered a probable assumption, and the name has been provisorily retained. If there be an unconformity by erosion, it would be most naturally placed between this and the Shale series below, because of the variation in thickness of this siliceous mem ber, it being entirely wanting on the northern flanks of the range; but no direct evidence of erosion could be detected and the conglomerate has not the characteristics of a true basal conglomerate. In the Duchesne valley the Shale series consists of about 1,200 feet of thin-bedded, dark, argillaceous shales, in which we were unable to detect the pyrites to which Mr Berkey refers. Their best exposures are in Hades Creek and Iron Creek ravines, adjoining the fault. They have no rela tion, as the latter name might suggest, to the deposits of iron ore which occur, as Mr Boutwell has noted, in the Wasatch limestones much higher in the geological column. The thickness of the Shale series is also variable, being nowhere so great as in the Duchesne valley; but it is never entirely wanting, as is at times the Ogden quartzite. In my original field notes I find mention of a few hundred feet of greenish shales observed at various points, sup posed to be part of the upper members of the Uinta quartzite. The Iron Creek fault has not the structural significance that Mr Ber key would assign to it. It can only be traced 7 or 8 miles on either side of the Duchesne valley, though similar strike faults occur at various points along the southern flanks of the range, more frequently where the strata have taken a sudden downward bend, so that the existence of the fault is less evident than on the Duchesne. In spite of its striking prom inence in the valley bottom, the Iron Creek fault could not be detected on the plateau-like summit of the spurs on either side of the Duchesne, un less one knew of its existence and made a special search for it; for on the Downloaded from gsabulletin.gsapubs.org on July 31, 2015

298 S. F. EMMONS----UINTA MOUNTAINS east, as Mr Berkey himself remarks, the Ogden quartzite is in juxtaposi tion to the Uinta quartzite and perfectly conformable in angle, and on Rhodes spur, where the former caps a bold escarpment facing north, overlooking the interior plateau, the shales are effectually concealed by a talus of huge blocks of greenish white Ogden quartzite, likewise con formable. Above the Wasatch series is a great siliceous member consisting largely of white calcareous sandstones and gray quartzites, which I correlate with the Weber quartzite,* and for which Mr Weeks estimates an aggre gate thickness of 2,200 to 2,700 feet. This is presumably the series of beds at the base of which Mr Berkey placed his main unconformity; but in spite of a most careful search, continued by Mr Weeks throughout his circuit of the range, we were unable to find the basal conglomerate on which Berkey’s scheme of corre lation is mainly based. Negative evidence is confessedly somewhat dan gerous ground upon which to deny the existence of an unconformity by erosion, since such unconformity involves no discrepancy of angle, and the positive evidence of overlap is not necessarily present, while it is rare, even in long and well exposed canyon sections, to get unmistakable evidence of the unevenness of an old eroded surface in the hollows of which the later beds were deposited. In the present case their superior resistance to erosion and the slowly steepening angle of dip have com bined to leave patches of the Weber beds in abnormally high positions on the spurs (see map, figure 2), which probably led Mr Berkey to suppose they came there by overlap. Even did such an unconformity exist, how ever, his scheme of correlation based on it would fail, since it assumes that it is the same unconformity that Powell observed in the canyon of Oreen river; but there the Eed Wall limestone, which corresponds to the Wasatch of the Duchesne, lies above this unconformity. Even Mr Ber key’s hypothesis of a sea that was slowly retreating westward and then rapidly readvancing could hardly account for the same beds being de posited above the erosion interval in one place and below it in another. Above the Weber quartzites are cherty limestones, followed by cal careous sandstones and argillaceous shales, in which the calcareous ele ment decreases upward until they end in a series of deep red shaly beds which, owing to their easy erosion, are apt to form hogback valleys.

* It has been considered advisable to use the old Fortieth Parallel names of forma tions and not attempt to make subdivisions characterized by local names until the region is areally surveyed. For the great central quartzite series Powell’s name, Uinta, has been retained, because it is not only the most appropriate, but also possesses priority in published description. As used on the Fortieth Parallel maps, this name indicated simply an area of Tertiary beds of probable different ages, but not yet differentiated. Downloaded from gsabulletin.gsapubs.org on July 31, 2015

STRUCTURE 299

This series has a thickness of about 2,500 feet and carries an Upper Carboniferous and Permian fauna. It is in this series that the uncon formity by erosion, if it exists, is likely to occur. It is suggested by the apparent overlap of the beds; moreover, a widespread unconformity is known to exist at this horizon in Colorado and elsewhere. Above these in typical development are the light red, thin-bedded sandstones, generally classed as Triassic, which in turn are succeeded by shales and limestones carrying characteristic Jurassic fossils. The accompanying map (figure 2), of which the topographic base is a copy of a portion of the Hayden Peak quadrangle of the Forest Reserve Survey by the U. S. Geological Survey, shows the distribution of the above described beds as far as they occur on the area mapped. Unfor tunately the map extends only a few miles south of the Iron Creek fault, so that a large part of the Paleozoic exposures do not appear on it.

S t r u c t u r e

In the area represented the beds do not strike due east and west, but to the north of east on the east side of the valley and to the north of west on the west side, which means that the valley runs approximately in the axis of a secondary anticlinal fold, with axis at right angle to that of the main anticline. In dip the beds steepen to the southward from the aver age angle of 5 degrees in the Uinta quartzite to 10-17 degrees in the area mapped; then to 25 degrees just south of it, and finally to 45 or even 60 degrees along a varying line that follows the southern flanks of the ranges. A typical cross-section of the range is given in figure 2, which is reduced and somewhat generalized from an actual section drawn to natural scale on a line following the top of the spur east of the Duchesne. Just north of the main crest of the range there is generally found to be a sharp break line in the Uinta quartzites, on the south of which they in cline from 2 to 5 degrees southward, and on the north dip steeply north ward up to angles of 45 degrees or more. There has evidently been fault ing in the region where this remarkable change of dip takes place, but, owing to the similarity in lithological constitution of the rocks on either side, neither the throw nor even the location of the fault can be deter mined. I t is not, however, continuous along a given east and west line, as seems to have been assumed by Powell, who probably reasoned from the most strongly marked of these faults, which runs along the northern edge of the Red Creek Archean body, in the Browns Park region; this fault, however, has a strike of from 16 to 20 degrees to the north of east and crosses Green river to the south of Horseshoe canyon; hence Downloaded from gsabulletin.gsapubs.org on July 31, 2015

300 S. F. EMMONS----UINTA MOUNTAINS could not coincide with the faults north of the crest, which probably are arranged en echelon. Along the southern flanks the faulting is apt to take place near the sudden steepening of the dip, which is observable in most' every cross-section, and beyond which the beds resume their former low angle and extend southward under the Tertiaries in a broad, shallow syncline. Thus the. uppermost of the Mesozoic beds involved in the orig inal Uinta arch, the Laramie formation, first reaches the surface again 100 miles to the south in the Book cliffs, just north of the Bio Grande Western railway. The sudden steepening of the dip on a given line along the flanks of a mountain uplift is a common phenomenon, and notably well developed along the east face of the Front range of Colorado, and can best be explained as the result of a tangential shove, as illus trated by some of Bailey Willis’s experiments in mountain building. On this hypothesis the faulting would be an expression of the relief of strain along lines of extreme folding tension.

Correlation

Having had an opportunity in recent years of personally examining the Grand Canyon section, on which Powell based his Green River Pale ozoic section in the Uintas, I am better able to correlate the latter with that exposed in the Duchesne region as shown above. My interpretation would be as follows: The remnants of red beds on the Coconino plateau correspond to the Permo-Carboniferous beds on the Duchesne; the Upper Aubrey limestone to the cherty limestone immediately above the Weber quartzite; the Lower Aubrey to the Weber quartzite itself, and the Red Wall to the Wasatch limestone. In either region there is uncertainty, through want of fossil evidence, as to the Devonian and Silurian. In the Grand Canyon region a Devonian fauna has been discovered in a thin series of rocks separated from the Red Wall limestone by a slight uncon formity, but the Silurian is apparently wanting. In the Uintas no fossils have yet been found below the Wasatch limestone. The Ogden quartzite, whose name has been temporarily retained for the Duchesne section, has in the Wasatch recently been determined to lie below beds of Ordovician age. It is probable, therefore, that both Devonian and Silurian are wanting in the Uintas, and that the Tonto of the Grand canyon is repre sented by the Ogden quartzite or the Shale series, or by both together. Powell’s Lodore series is supposed to represent the Tonto series of the Grand canyon, though in his Uinta report he said Carboniferous fossils had been found in it, which was evidently an error, probably caused by a displacer it of labels during transportation. Downloaded from gsabulletin.gsapubs.org on July 31, 2015

CORRELATION 301

The Uinta quartzites occupy a position corresponding to the Pre- Cambrian series in the Grand canyon which Powell included under the general name of Grand Canyon series. This has since been subdivided into the Chuar, Grand Canyon, and Vishnu series, each separated by an unconformity, only the lower member of which, the Vishnu, resembles lithologically the Uinta quartzite. Powell failed to recognize the Permo-Carboniferous in the Uintas, as he did in the Grand canyon, but in other respects his geological column in the Uintas above the Carboniferous corresponds fairly well with that of the Fortieth Parallel, though the formations are given different names and their lines of diversion are placed at somewhat differing horizons. The greatest uncertainty that still remains is in regard to the proper correlation of the Ogden quartzite and the Shale series. If we correlate with the Wasatch section, they correspond best with the Cambrian of the Big Cottonwood section; if with the Grand Canyon section, they fit best the Tonto, which consists of shales and sandstones. There is still some uncertainty as to the location of Powell’s uncon formity in the western Uintas, if indeed it exists there. Owing to the want of precision in his published statements,'it is difficult to verify his observations in the field. As already stated, I think its most probable place is between the Ogden quartzite and the Shale series. The Uinta quartzites I regard as undoubtedly of Pre-Cambrian age, but, like most Pre-Cambrian formations in the West, which are widely separated and generally barren of fossils, its exact correlation will for a long time probably remain in doubt.

Or ig in of Green R iver

The statement of Powell, in his volume “Exploration of the Colorado River of the West,” with regard to Green river, to which he assigns an antecedent origin, thereby furnishing a striking proof of the slowness of the movement of mountain uplift, picturesquely comparing the contem poraneous uplift of the Uinta mountains and the corrasion of the Green River canyons with movement of a saw-log relative to a buzz-saw, have been accepted and quoted by many writers of text-books on geology. My theory that it is a superposed river, based on the occurrence of remnants of Wyoming conglomerate (Bishop Mountain conglomerate of Powell) resting unconformably on all underlying formations, and so situated that when connected together they must have entirely covered that part of the range through which the Green River canyons are now cut, has re ceived less notice; nevertheless it has been accepted by such authorities as Downloaded from gsabulletin.gsapubs.org on July 31, 2015

302 S. F. EMMONS— UINTA MOUNTAINS

Professor Ed. Suess and Professor Wm. M. Davis. I have elsewhere* stated some of the physical impossibilities which Powell’s hypothesis in volves, and will therefore not enlarge upon them here. I have always been a firm believer in the theory that the uplift of a mountain chain is immensely slow, and, further, that it is continuing at the present day, as I have had occasions to demonstrate by facts disclosed in the under ground workings of mines. In the Uinta mountains it is easy to find facts in support of this theory without resorting to the hypothesis of the antecedent origin of Green river. As is well known, the forming of the Uinta arch commenced at the close of the Cretaceous, as is evidenced by the fact that the flanking Tertiary beds lap unconformably over the up turned edges of the older strata, which when exposed are seen to stand at angles of 30 degrees and upward. There are three series of Tertiary beds filling wide basins both north and south of the Uintas—the Wasatch (or Vermillion Creek of the Fortieth Parallel), the Green River, and the Bridger formations, all of Eocene age and with an erosion interval be tween each. Now, while each of these series of beds occupy a practically horizontal position throughout their basins, at the very edge of the Uinta mountains they can be seen to be slightly upturned against their flanks, the lowest series at the greater angle, 15 degrees or even 20 degrees in places, and the more recent beds correspondingly less, which means that the continued rising of the mountain mass had dragged up the adjoining edges of the beds resting against their flanks—a movement which, being continuous, has necessarily been greater in the case of the older beds.

* Science (new series), vol. vi, July 2, 1897, no. 131. Downloaded from gsabulletin.gsapubs.org on July 31, 2015 Geological Society of America Bulletin

Uinta mountains

SAMUEL FRANKLIN EMMONS

Geological Society of America Bulletin 1907;18, no. 1;287-302 doi: 10.1130/GSAB-18-287

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Notes