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

typically mapped where lava flows dammed local washes causing ponding ofmixed colluvial and alluvial sediment; distal, finer-grained parts form broad, openmeadows; thickness uncertain, but likely less than about 20 feet (6 m) thick.QceColluvium and eolian sand (Holocene to upper Pleistocene) − Poorly tomoderately sorted, angular, clay- to boulder-size, locally derived sediment ―partly covered by a veneer of eolian sand ― deposited by slope wash on moderateslopes and in shallow depressions in the Red Hills graben south of Parowan Gap;colluvial debris is derived from the Red Hills lava flow and underlying NavajoSandstone; probably less than 20 feet (6 m) thick.Qmtc Talus and colluvium (Holocene and upper Pleistocene) – Poorly sorted, angularto subangular, cobble- to boulder-size and finer-grained interstitial sedimentdeposited principally by rock fall and slope wash on steep slopes throughout thequadrangle; includes minor alluvial sediment at the bottom of washes; generallyless than 30 feet (9 m) thick.Qmsc Landslides and colluvium (Holocene and upper Pleistocene) – Landslides andcolluvium impractical to differentiate at this scale; typically mapped below thewest rim of the Markagunt Plateau, where Upper Cretaceous strata, locallycovered by basalt talus and colluvium, reveal evidence of slumping and soilcreep; as much as several tens of feet thick.QlaQlaoLacustrine sediment and alluvium (Holocene) − Not exposed, but forms themeadow of Blue Spring Valley about 2 miles (3 km) southwest of PanguitchLake, which we interpret to be moderately to well-sorted, thinly bedded, lightgrayand light-brown, fine-grained sand, silt, and clay derived principally fromBrian Head strata in the Bunker and Deer Creek drainages; upper surface ismarked by numerous small stream channels and meander cutoffs; also mappednear the east end of Navajo Lake, where it consists of fine-grained sedimenteroded from the red member of the Claron Formation.Blue Spring Valley was flooded to form a shallow reservoir followingcompletion of the Blue Spring Valley dam in the late 1800s or early 1900s; thesmall dam was breached by 1917 (Ipson and Ipson, 2008). The valley is nowdrained at its north end by Spring Creek, which may have formed in response tothe Miller Knoll lava flows that blocked the original outlet at the southeast end ofthe valley possibly as late as middle Holocene time. Lacustrine sediment andalluvium is likely several tens of feet thick in Blue Spring Valley, and may overliestream deposits of ancestral Bunker Creek, which may have exited the southeastside of the valley prior to being blocked by the Miller Knoll lava flows.Older lacustrine sediment and alluvium (Holocene and upper Pleistocene) −Similar to lacustrine sediment and alluvium (Qla), but forms incised surfaces 5 to10 feet (2-3 m) above the meadows of Blue Spring Valley; likely several tens offeet thick.10