Geologic mapping of the Jessen Butte 7.5 minute quadrangle and the gathering of structural data throughout the quadrangle was used to determine the paleostress regime during the Laramide Orogeny along the north flank of the Uinta Mountains. The Henrys Fork thrust fault and the Uinta thrust fault are major north bounding faults and within the Jessen Butte quadrangle these faults transfer deformation from one to the other. The Jessen Butte thrust fault is a fault splay that splits off from the Henrys Fork thrust fault. Complex fold geometries were created by the interaction of the faults. Bedding plane orientation, mode I fracture orientation, and fault kinematic indicators were measured throughout the quadrangle. A shortening direction to the NE was recorded by all of these different types of measurements, which match with the proposed regional stress field for the Laramide Orogeny. In a few cases N-S shortening was also recorded in the data, which may be from the local stresses in the area due to pre-existing weaknesses in the basement rocks. Finally, for creation of the cross sections, a positive flower structure model best fit the fold geometry of the rocks in the Jessen Butte quadrangle. This type of fold forms in areas which experience strike-slip motion. This suggests that, at least along the north side of the Uinta Mountains, deformation occurred in a uniform stress field during the Laramide Orogeny, with some influence from the pre-existing weakness inherited from the Precambrian basement.



College and Department

Physical and Mathematical Sciences; Geological Sciences



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Uinta Mountains, structure, Jessen Butte, Manila, positive flower structures



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Geology Commons