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Downloaded from gsabulletin.gsapubs.org on July 31, 2015 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