Structural Geology of the Southern Part of Elkhorn Mountain, Bannock Range, Idaho
Date of Award:
Master of Science (MS)
Clyde T. Hardy
The area of souther Elhorn Mountain, a previously unmapped area, is located north of Malad City, Idaho, in the Bannock Range. The mapped area is within the Basin and Range province. The mapped area measures 5.9 miles in the north-south direction and approximately 8.8 miles in the east-west direction. The oldest stratigraphic unit, in the mapped area, is the Ute Formation of Middle Cambrian age. Other units of Cambrian age, in ascending order, are: Blacksmith Formation, Bloomington Formation, Nounan Formation, and St. Charles Formation. The units of Ordovician age are the Garden City and the Swan Peak Formations. The youngest unit of Paleozoic age, in the mapped area, is the Fish Haven-Laketown Formation of Ordovician-Silurian age. The Paleozoic units are composed predominantly of limestone and dolomite; some unites contain varied amounts of quartzite and shale. The Salt Lake Formation and associated volcanic rocks of Tertiary age are present locally in the mapped area. Lake Bonnevill Group, colluvial deposits, and alluvial deposits, all of Quaternary age, are also present. A thrust fault, folds, and normal faults are present in the mapped area. A bedding-plane thrust fault is present between the Bloomington and Nounan Formations. A broad anticline is suggested by the attitudes of the Paleozoic rocks of southern Elkhorn Mountain. Small-scale folds are exposed locally. The normal faults are of two major trends, northwest and north. These fault sets are contemporaneous and they cut Salt Lake Formation. These sets intersect and form numerous fault blocks. The normal faults cut the thrust fault and the fold. Thus, the thrust fault and the fold are isolated within various fault blocks throughout the area. The marginal normal faults are responsible for the present topography. Remnant blocks of a major landslide are also present. The structural features of the area are the result of two major structural events, the older Laramide orogeny and the more recent Basin and Range faulting. The Laramide orogeny, active from Late Jurassic to early Eocene, was responsible for the thrust faulting and folding. The Basin and Range faulting, active from Oligocene to Holocene, was responsible for the normal faults and the landslide. Marginal normal faults are probably active at the present time. (101 pages)
De Vries, George A., "Structural Geology of the Southern Part of Elkhorn Mountain, Bannock Range, Idaho" (1977). All Graduate Theses and Dissertations. Paper 1902.
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