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North Flank of the Uinta Mountains, Utah

J.H. Clement
J.H. Clement
Shell Oil Company
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January 01, 1983


The Uinta Mountains are an elongate, east to west trending range consisting entirely of metasedimentary and sedimentary rocks arched in a broad, asymmetrical anticline in northeastern Utah and adjacent northwestern Colorado. As Rocky Mountain ranges go, the Uintas are somewhat unique, trending east to west in a foreland region where most ranges strike generally north to northwest, and are cored by Precambrian crystalline basement complexes.

Late Precambrian quartzites, metaquartzites, sandstones, and shales comprise the broad core of the Uintas. These rocks make up the crest of the range and the broad interfluves that descend on both sides of the crest far down the flanks of the range. This Precambrian terrane is exposed for a distance of over 193 km (120 mi) in an east to west direction and an average of 29 km (18 mi) in a north to south direction. Cropping out along the topographically lower flanks of the range are Paleozoic and Mesozoic sedimentary rocks with an aggregate thickness of nearly 4,572 m (15,000 ft). The major flanking basins, Green River (north) and Uinta (south), are filled with Tertiary fluviatile and lacustrine sediments which lap on the flanks of the range.

A complex system of faults demarcating the boundary between the north flank of the uplift and the adjacent Green River basin has been mapped in exposed surface strata by geologists during the 115 years since Major John Wesley Powell first traversed the Range in 1868. The geometry of these boundary faults has been a matter of much controversy. W.R. Hansen's comprehensive works (1955-69), describe the reverse (30 to 70° nature of the observed flank faults, and Ritzman (1959), in a summation of faulting in the area, proposed that the Uinta fault is inclined at a very low angle (less than 10° to the south in some areas. However, the concept of normal faulting along the Uinta north flank persisted into the 1960s as evidenced by its depiction on the Tectonic Maps of the United States (1962) and North America (1969) which both show the Uinta Uplift bounded essentially by normal faults. This confusing interpretation may have been influenced by the existence of a number of vertical and high-angle, range-parallel faults that are mapped within the outcrop area of the Precambrian metasediments (see "crest fault" shown on geological section), but these are not the major boundary faults.

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AAPG Studies in Geology

Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces

A. W. Bally
A. W. Bally
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American Association of Petroleum Geologists
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Publication date:
January 01, 1983




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