Geologic map of the Smelter Knolls West quadrangle, Millard County, Utah (M-148)
By: L. F. Hintze and C. G. Oviatt
This quadrangle includes the southeastern tip of the Drum Mountains, the eastern part of the Little Drum Mountains, a portion of the Sevier Desert transected by a swarm of Quaternary fault scarps, and the western side of the Smelter Knolls rhyolite dome and lava flow complex. Oldest rocks are Middle Cambrian carbonates and shales of the Chisholm, Whirlwind, Swasey Limestone, Wheeler, and Pierson Cove formations. Regionally, these strata aggregate about 2,600 feet in thickness but because of faulting, less than half that amount is exposed in the map area. The east side of the Little Drum Mountains exposes a gentle homocline made up almost entirely of Eocene volcanogenic rocks that lie with angular unconformity over the structurally more complex Cambrian strata. The oldest volcanic rock is the Drum Mountains Rhyodacite, about 1,000 feet thick and about 42 million years old. The rhyodacite is overlain by the Little Drum Formation which is about 3 million years old and 2,400 feet thick. A series of andesitic ash-flow tuffs and tuffaceous deposits make up more than half of the Little Drum Formation. The remainder is composed of a series of coarse, poorly sorted conglomerates that are intercalated with the tuffs. These conglomerates include rounded to subangular quartzite and andesite boulders up to several feet in diameter that were most likely derived from the Drum Mountains area to the northwest.
Pages: 21 p.
Plates: 2 pl.
Location: Millard County
Media Type: Paper Map