Geologic map of the Keg Pass quadrangle, Juab County, Utah (MP 99-4)

By: M. A. Shubat and G. E. Christenson

The Keg Pass 7.5 minute quadrangle is in west-central Utah and includes the western part of Keg Mountain. The oldest rocks exposed in the quadrangle are Cambrian quartzite and limestone. These rocks were deformed during the Sevier orogeny, which produced at least two thrust faults in the quadrangle. Most of the quadrangle is underlain by Tertiary volcanic and intrusive rocks. Several calderas and cauldrons are in and near the Keg Pass quadrangle; they are part of a large, late Eocene to early Oligocene igneous center that spans the Thomas Range, Keg Mountain, and northern Drum Mountains. The major igneous events in the quadrangle were: (1) eruption of the Dead Ox Tuff and subsidence of the associated Flint Spring cauldron; (2) eruption of the Keg Tuff, subsidence of the associated Keg cauldron, and intrusion of granodiorite; (3) eruption of the Mt. Laird Tu ff and collapse of the associated Thomas caldera; (4) eruption of the Joy Tuff, subsidence of the associated Dugway Valley cauldron, and intrusion of rhyolite porphyry; (5) eruption of the Dell Tuff from an unknown source; and (6) eruption of late Miocene Topaz Mountain Rhyolite from scattered local vents. Mineral occurrences in the quadrangle probably formed during this igneous activity and consist of volcanic-hosted gold prospects, polymetallic veins, and precious metals-enriched jasperoid bodies. Deposition of exposed sediments during Quaternary time was dominated by Lake Bonneville, which covered much of the northern and western parts of the quadrangle. Other surficial deposits include stream alluvium, colluvium, and alluvial-fan and eolian deposits. Potential industrial mineral and rock resources in the quadrangle include sand and gravel, cement rock, high-calcium limestone, zeolite minerals, crushed stone, and dimension stone.

Other Information:
Published: 2000
Pages: 28 p.
Plates: 2 pl.
Scale: 1:24,000
Location: Juab County
Media Type: Paper Map