Structural Analysis of the Shell Canyon Area, Bighorn Mountains, Wyoming

The area is divided by Shell Canyon into two structurally dissimilar regions corresponding to the northern and central structural provinces of the Bighorn Mountains. The mountain trend changes abruptly from an N-S strike south of Shell Canyon to N 60°W north of the Canyon. The northern part of the area has steeper dips and fewer flexures, the uppermost being a chevron fold. The only fault in the north part is the Horse Creek Fault. It is vertical, runs oblique to axial traces for four miles in an E-W direction, attains a maximum of 450 feet of throw and may have strike-slip movement. South of the Canyon the front is lower, with more numerous and broader flexures. The upper flexure is concentric. There are two low angle thrusts dipping west with 45 feet and 210 feet of dip-slip. There are also three vertical faults. Planar fractures in the Paleozoic strata show definite preferred orientation. Each fracture pattern has one dominant direction which is interpreted as shear. This set is usually perpendicular to axial traces. The thrust faults in Trapper Creek agree in strike and dip direction with a weak set of fractures. The vertical faults in White Creek are aligned with the dominant set of fractures and are of similar origin