Date of Award:
Master of Science (MS)
Clyde T. Hardy
The west central part of the Malad Range is located in south-eastern Idaho. This area was the site of thick marine deposition in the early Paleozoic period. In the Tertiary and Quaternary periods continental deposition occurred, covering the Paleozoic rocks. Quartzite and shale units of the Brigham Quartzite are found near the base of the Cambrian section. Carbonate with shale interbeds is found in the middle and late Cambrian units. Limestone and silty limestone are found in the early and middle Ordovician time overlain by the middle Ordovician Swan Peak Quartzite. The Laketown Dolomite includes units of late Ordovician and Silurian age. Paleozoic units younger than Silurian and and Mesozoic units are not found in the mapped area. Red conglomerates mark early Tertiary deposition, and water-lain tuff, fresh-water limestone, conglomerate and sandstone are of middle and late Tertiary age. Tertiary-Quaternary rocks, found in the mapped area, are composed of deposits of boulders resting on older Tertiary and Paleozoic rocks. These deposits show rough polygonal structures and stone stripes. Quaternary deposits are composed of sediment from the Late Pleistocene Lake Bonneville and Quaternary alluvium.
Northwest-trending faults, northeast-trending faults, and north-trending faults are found in the mapped area, with northwest-trending faults predominating. The northwest-trending faults are high-angle faults and have resulted in Tertiary rocks being faulted against lower Paleozoic rocks. Northeast-trending faults are roughly parallel and predate the middle and late Tertiary rocks. North-trending faults are high-angle faults involving both Paleozoic and Tertiary rocks. One northwest-trending fault has evidence of horizontal movement. The structures are assigned to three periods of movement: 1. early Cretaceous to early Tertiary, 2. late Tertiary to middle Tertiary, 3. middle Tertiary to Recent.
Wach, Phillip H., "Geology of the West-Central Part of the Malad Range, Idaho" (1967). All Graduate Theses and Dissertations. 6648.