This thesis, having been approved
by the special Faculty Committee, is accepted
by the Graduate School of the
University of Wyoming,
in partial fulfillment of the requirements
for the degree of Master of Science
Robert H. Bruce (signed)
Dean of the Graduate School
Date: May 8,
1969
QUATERNARY GEOLOGY OF THE BURNT FORK
AREA, UINTA MOUNTAINS,
SUMMIT COUNTY, UTAH
by
Mark J. Schoenfeld
A Thesis
Submitted to the Department
of Geology and the Graduate School
of the University of Wyoming in Partial
Fulfillment of Requirements for the Degree of
Master of Science
University of Wyoming
Laramie, Wyoming
March, 1969
ABSTRACT
The Burnt Fork drainage
area, on the north flank of the Uinta Mountains, has well‑preserved
Tertiary and Quaternary geomorphic features and Pleistocene
glacial till, Remnants of Oligocene and Pliocene erosion surfaces exist at
elevations greater than 9,500 and 10,400 feet; respectively. Two pre‑Wisconsin surfaces are
found at elevations less than 9,000 feet:
the Burnt Fork surface, formed by fluviatile
erosion and redeposition of an Eocene
conglomerate, and the Eastern surface, a local pediment.
Glacial features include moraines of Bull Lake, Pinedale,
and Neoglacial age~ Pre‑Wisconsin till may also
be present. At least two Bull Lake and
three to five Pinedale advances are represented; Neoglacial deposits
include moraines of one Temple Lake stade and periglacial
Gannett Peak material. The cirque area appears to be in a youthful stage, and cirque morphologies indicate different stages of cirque development.
A tentative theory for these differences suggests that Island Lake and
Burnt Fork Lake cirques developed first, through ice
accumulation and erosion at the heads of major stream valleys. Uplift during Pinedale time
allowed ice to accumulate in the higher area between the cirques,
resulting in the later development of Triplett Lake and Shafe Lake cirques.
Bull Lake and Pinedale terraces are found solely on
the east side of the Burnt Fork valley below the Lower Pinedale front. The terrace sequence suggests a relatively
short interval between the Lever and Middle Pinedale advances and possible
contemporaneous regional uplift, greater in the western part of the range. Periglacial features include rockfalls,
stone nets and streams, solifluction lobes, and protalus ramparts.
CONTENTS
Structural and
Stratigraphic History
Bedrock Geology of
the Burnt Fork Area
PRE‑WISCONSIN
QUATERNARY GEOLOGY
Descriptions of
Individual Cirque Areas
Theories of Terrace
Development
LIST OF ILLUSTRATIONS
Plate 1a. Quaternary Geology of
the Lower Burnt Fork Area, Uinta Mountains, Utah
Plate 1b. Quaternary Geology of
the Upper Burnt Fork Area, Uinta Mountains, Utah
PLATE 3. PRE‑WISCONSIN
FEATURES
Figure 2. Terrace profile
sketch Map
Burnt Fork Creek rises in a small
unnamed lake, 40°49'130" N. latitude, 110°59" W. longitude, hereafter
called Meeks Lake, on the north flank of the Uinta Mountains, five miles due
east of South Burro Peak. From there it
flows one‑half mile northwest into Burnt Fork Lake, then in a more
westerly direction for roughly one mile before turning and flowing north‑northeast
down the north flank of the mountains to its confluence with Henrys Fork just north of the Utah‑Wyoming border. The area studied included the Burnt Fork valley and, to a lesser extent, adjacent
highlands east of the creek.
Accessibility
to the area in very limited. Dirt roads and trails leading to the cirque areas were
largely destroyed by heavy flooding in recent years. Intermediate elevations and cirque areas are now accessible
either by pack trail or by jeep along dirt roads extending south and
west from Utah Route 165 (the Sheep Creek Road). However, most are blocked
by snow and spring thaws and are inaccessible after heavy rains. Ranch roads give access to the lower part of the area.
Although no previous detailed studies of the Quaternary geology of the Burnt Fork area exist, Powell (1876) and Clarence King (1878) recognized glacial material in the valleys of the north flank of the Uinta Mountains. King (P. 470) noted "well defined glaciation and moraine material down to between 8,000 and 9,000 feet" along Bear River, Smiths Fork and Blacks Fork. Atwood (1909), in his reconnaissance of the Uinta and Wasatch Mountains, included a brief resume of the glacial geology of the Burnt Fork area, noting evidence for two and perhaps three glacial advances. Bradley (1936) separated the glacial chronology of the north flank of the Uintas into three stages which he correlated with the chronology proposed by Blackwelder (1915) for the Wind River Mountains.
Table 1. Comparison of Glacial
Chronologies Used by Different Workers in the Wind River and Uinta Mountains
Bradley mentioned the Burnt Fork area but gave few details. Since Bradley's work no one has published any work on the Quaternary geology in the northern Uinta Mountains,
Field work was carried out in the summer of 1968 using advanced and final copies of U.S.G.S. topographic maps surveyed in 1962 and 1966, scale of 1:24,000.[1] Terrace and moraine heights were measured with a Brunton Compass. Heavy forest cover, lack of accessibility, and inclement weather limited investigation of certain areas.
1However, all section locations are given with regard
to the U.S.G.S. Gilbert Peak, Utah‑Wyoming, Quadrangle, 1905, scale of
1:125,000.
members of the faculty of the Department of Geology at the University of Wyoming, especially
Dr. D. L. Blackstone and Dr. P. 0. McGrew, provided helpful advice and information, as did
Dr. J. D. Love of the U. S. Geological Survey and Prof. Eugene P. Kiver of the Department of Geology, Eastern Washington University.
I also wish to thank Mr. and Mrs. Ruel Triplett of McKinnon, Wyoming; Mr. and Mrs. Charlie Meeks of Burntfork, Woming; and the owners of Spirit Lake Lodge, Utah, for their hospitality and assistance during field work. Mrs. Peggy Deaver typed the manuscript; Gary Sandberg of the University of Wyoming assisted in the preparation of the maps and diagrams. A grant from the University of Wyoming through the Charles S. Hill Memorial Scholarship Fund is gratefully acknowledged. My wife, Chantal, provided encouragement during the writing of this report.
Structurally the Uinta Mountains are a broad, flat‑topped anticlinal arch, exposing Precambrian rocks along the range's crest and rocks of Paleozoic to Tertiary age along the flanks. The higher parts of the range are eroded into impressive cirques and glacial throughs, and streams have incised canyons as much as 2,000 feet below the surrounding summit levels, forming a rugged topography. Floral zones, in ascending order, include juniper, shrubs, aspens, pine, spruce‑fir, with alpine shrubs and grasses above timber line (Untermann, 1964).
A brief summary, based essentially on
the work of Forrester (1937), for the pre‑Cenozoic development of the
Uinta Mountains follows.
Precambrian history of the Uinta region involved deposition in the Uinta trough, an east‑west trending arm of the Wasatchian geosyncline, of two major units: (1) the Red Creek Quartzite of Archean age, and (2) conformable above it, the Uinta Mountain Group (or Uinta Series) of Algonkian age. In turn these units are overlain disconformably by Cambrian shales and quartzites (Cohenour, 1959). The Cambrian rocks lie with well‑developed angular unconformity below limestones of Mississippian age and later sediments. South of the Uinta Mountains Mississippian or Mesozoic sediments directly overlie rocks of Archean age (Butler et al, 1920), thus indicating a late Precambrian and early Paleozoic source for sediments in the Uinta trough. During Carboniferous time the rising Uncompaghre Range of the "Ancestral Rockies" provided a southeastern source of material for the trough. A continuous sequence of shallow‑water, near‑shore and eolian deposits ranging from Mississippian through Upper Cretaceous in age interfingers with thicker marine in facies deposits towards the west (Untermann, 1955).
Laramide deformation initiating the Uinta Mountains began in late Cretaceous time in response to "deepseated compressive or torsional stresses, acting from southerly and southwesterly directions on the sediments deposited in the Uinta trough" (Forrester, 1937, p. 655). The Uinta arch became a broad, low‑dip anticline, slightly asymmetrical towards the north, with a total uplift for the first stage of the Laramide orogeny estimated between 10,000 and 12,000 feet. However, contemporaneous erosion was removing sediments from the central part of the range and depositing then in adjacent basins, and thus the height of the mountains never approximated the fall amount of uplift. These sediments were themselves eroded and redeposited during the Eocene as the Wasatch Formation, though local remnants of Paleocene Fort Union Formation remain on the east side of the range. After uplift ceased the region was reduced to a low, rolling surface at about the close of the Eocene.
During the late Eocene and early Oligocene, vertical uplift and large‑scale faulting of the Uinta Mountains tilted and warped the Eocene sediments, bringing them into contact with Paleozoic and Mesozoic units. Uplift of the center of the range during this time was approximately 25,000 feet, with greatest uplift at the West end of the range. Major faults of this period (such as the Uinta Fault, Henrys Fork Fault, North Flank Fault, etc.), are normal, high‑angle strike faults, formed in response to tensional, vertical stresses believed to be associated with emplacement of a batholithic core in the area previously deformed by folding (Forrester, 1937). A period of erosion followed, during which the two major erosion surfaces of the Uinta Mountains, the Gilbert Peak surface (Late Oligocene‑Early Miocene) and the Bear Mountain surface (Late Miocene‑Early Pliocene) were formed (Bradley, 1936). During Early Pliocene time an epeirogenic uplift affected the region as well as the Colorado Plateau, Wasatch, and Great Basin Ranges. This last period of uplift is estimated to have been between 8,000 and 10,000 feet and gave the Uinta Mountains a total uplift of approximately 45,000 feet, though less than one‑third of this is topographically expressed.
Precambrian rocks of the Burnt Fork region are mainly medium‑grained, reddish‑purple quartzites called the Mutual Formation of the Uinta Mountain Group (Stokes and others, 1963). The crest of the Uinta Mountains is developed in this unit for many miles to the east and west of Burnt Fork and is widely exposed in the cirque walls above the 10,000 foot contour. Preserved sedimentary structures such as crossbedding, convolutions, and ripple marks indicate a probable shallow‑water or fluviatile origin prior to low‑grade metamorphism. Kinney (1955) observed similar sedimentary structures in this unit in the Duchesne River‑Brush Creek area along the south flank of the range.
Interbedded shales and quartzites of possible Precambrian age crop out near Burnt Fork along the eastern wall of an intermittent stream valley just north of McCoy Park. They are distinct from and younger than the Mutual Formation, but I do not know their exact age. Stokes and others (1963) indicate only Quaternary till at the described location. Three to four miles south of this outcrop the Red Pine Shale of Upper Precambrian age has been mapped (Stokes and others, 1963), although Weeks (1907) shows Lodore Formation (Cambrian) in approximately the same location. The units mentioned above are probably either Red Pine Shale or Lodore Formation cropping out farther south than previously recognized.
Downstream from an
