Interim Geologic Map of the West Part of - Utah Geological Survey

principally by debris flows, debris floods, and slope wash at the mouths of activedrainages and the base of steep slopes; locally reworked by small, ephemeralstreams; forms coalescing apron of fan alluvium and colluvium that cannot bemapped separately at this scale; typically 10 to 40 feet (3-12 m) thick.Qacfo Older colluvium and fan alluvium (Pleistocene) − Mapped below the west edgeof the Markagunt Plateau, where it consists of poorly sorted, boulder- to clay-sizesediment mostly derived from the Claron, Brian Head, and Isom Formations;deposited principally by debris flows, debris floods, and slope wash; typicallyforms a resistant cap on isolated hill tops and ridges underlain by UpperCretaceous strata, remnants of a once larger apron of sediment shed off theplateau and now preserved as deeply dissected inverted valleys; also forms broadbench, preserved in the Iron Peak graben, west of the town of Brian Head, whereit is locally exposed in the main scarp of a large landslide complex southeast ofSugarloaf Mountain (T. 36 S., R. 9 W., SE1/4SW1/4 section 8); also formsincised, isolated remnants south of Haycock Mountain, in the upper reaches of theClear Creek drainage, and a single deposit southeast of Brian Head peak; typicallyabout 20 to 30 feet (6-9 m) thick but larger deposits may locally exceed 50 feet(15 m) thick.QaeQeaAlluvium and eolian sand (Holocene and upper Pleistocene) − Moderately towell sorted, mostly light-reddish-brown silt and sand deposited by sheetwash andephemeral streams in small drainages and swales on the Henrie Knolls lava flowin the west-central part of the Henrie Knolls quadrangle; probably less than 10feet (3 m) thick.Eolian sand and alluvium (Holocene and upper Pleistocene) − Moderately towell sorted, yellowish-brown sand deposited by wind and locally reworked byephemeral streams; includes sand, silt, clay, and pebble to boulder gravel ofstream channels; mapped in the southern Red Hills; probably less than 20 feet (6m) thick.Qaec Alluvium, eolian sand, and colluvium (Holocene and upper Pleistocene) −Moderately sorted, light-reddish-brown and moderate- to dark-yellowish-brownsilt and sand and locally gravelly lenses deposited in swales and small drainageson and adjacent to the Henrie Knolls lava flow (Qbhk); the margins of thedeposits include significant colluvium derived from adjacent hillslopes developedon the Claron Formation and basaltic lava flows; soils developed on this unit havean argillic horizon 1 to 1.5 feet (0.3-0.5 m) thick of moderate-reddish-brownsandy clay and clayey fine-grained sand; typically less than 10 feet (3 m) thick,although deposits in the Cow Lake area, south of the Henrie Knolls flows, arelikely as much as 20 feet (6 m) thick.QcaColluvium and alluvium (Holocene to middle Pleistocene) − Poorly tomoderately sorted, angular, clay- to pebble-size, locally derived sedimentdeposited principally by slope wash and locally reworked by alluvial processes;9