Preliminary geologic map of the Parowan Quadrangle, Iron County, Utah (original) (raw)

Qac Alluvium and colluvium undivided (Holocene)-Pebbles, cobbles, and boulders in a silt and sand matrix. Poorly sorted. Composed of locally derived material deposited along streams, bordering flood plains, and local depressions. Estimated maximum thickness 5 m Of a Fan alluvium (Holocene) In Parowan Valley deposits are composed of poorly sorted pebbles, cobbles, and lesser amounts of boulders supported by silty sand matrix. Unit includes well rounded clasts derived from conglomerate beds of the Grand Castle (Tgc), Claron (Tc), and Brian Head (Tbh) formations. Approximate thickness 20 m QTfa Basin-fill deposit (late Pleistocene-Tertiary) Shown in cross section only. Includes basin-fill alluvial deposits approximately 470 m thick Qt Terrace alluvium (late Pleistocene)-Medium to coarse sand and pebbly to bouldery gravel. Found in the upper part of First Left Hand Canyon. Clasts are predominantly from Baldhills Member of Isom Formation (Tib) and also may have been eroded from landslide debris (QTli) hi Yankee Meadows. Estimated maximum thickness 20 m Qbw Trachy-basalt lava flows of Water Canyon (middle Pleistocene)-Black to darkgray, dense to vesicular, olivine-clinopyroxene bearing flows. Quartz xenocrysts common. Vent is located hi Water Canyon approximately 3 km east from eastern edge of Parowan Valley where flows fill a paleovalley. K-Ar whole rock date of lava is 0.45 ±0.04 Ma (Fleck and others, 1975). Table 1 shows chemical analysis and CIPW normative analysis. Thickness about 120m Qbwc Cinder cone of vent area-Composed of grayish-red scoria approximately 90 m thick Qbwd Feeder dike for basalt lava flows-Dark gray dense olivine-clinopyroxene bearing. Width about 2 m Qbh Breccia and basaltic dike of Second Hand Canyon (Pleistocene?)-Breccia and dikes are located hi Second Left Hand Canyon west of Henderson Hill. Breccia contains predominantly angular fragments of Claron Formation, Grand Castle Formation (?), cinder blocks of mafic rock, and sparse Needles Range Group rocks and Isom Formation hi a gray matrix. The breccia and dike may represent a vent complex. Approximate thickness 60 m Qdh Basaltic dikes Dikes are medium gray and fine grained, and contain olivine and clinopyroxene phenocrysts, rare quartz xenocrysts(?) and rare sandstone xenoliths. Dikes intrude the breccia and parallel mapped faults. Exposure may represent remnants of a vent breccia with feeder dike (roots of a cinder cone) Qp Pediment alluvium (middle? Pleistocene) Poorly sorted deposit composed of subangular pebbles, cobbles, and sparse boulders of Tertiary volcanic rocks, and Tertiary-Cretaceous sedimentary rocks hi a silty sand matrix. Deposited as thin veneers on fan-shaped surfaces. Estimated thickness 3-12 m