Date of Award:
Master of Science (MS)
Donald P. Olsen
The Wildcat Hills, located in Curlew Valley of northwestern Utah, are composed of a series of late Tertiary extrusive and dike rocks. Five volcanic rock types have been identified: an andesite, a rhyolite, a perlite, a basalt, and a welded tuff. Hydration of obsidian pellets contained in the flows has produced some of the perlite. Diatremes in the andesite attest to the high-volatile content and the explosive extrusion of some of the lavas. A compound basalt neck indicates that basalt was extruded at the Wildcat Hills and is not an erosional remnant of the basalt flow from the base of the Raft River Mountains which lie west of the study area.
The basalt was extruded during the late Tertiary. Initial extrusian was probably along early Basin and Range faults. The welded tuff was extruded next and was followed by the extrusion of the rhyolite after which caldera subsidence, was initiated and the remaining acidic magma was injected into the fractures to form a complex of short ring dikes of perlite. After the formation of the perlite dikes and perhaps concurrently with continued caldera subsidence, a magma of andesitic composition was extruded along caldera faults and possibly Basin and Range faults. Following extrusion of the magmas, the erosive processes began lowering the Wildcat Hills. More recently, Pleistocene Lake Bonneville was the principal agent of erosion and deposition, forming prominent terraces along the hills.
Howes, Ronald C., "Geology of the Wildcat Hills, Utah" (1972). All Graduate Theses and Dissertations. Paper 2116.
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