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

distal part of either the Midway Creek or Horse Pasture lava flows; the lavaflowed from west to east down the ancestral Duck Creek drainage and continuednortheastward to at least the Bowers Flat area at the west edge of the Asay Benchquadrangle; contains a long, open lava tube near Aspen Mirror Lake, just west ofDuck Creek village (U.S. Forest Service restricts access); lava flow is typicallypartly concealed by a veneer of unmapped surficial deposits of alluvial, colluvial,and eolian origin; age unknown, but it locally covers the Bowers Knoll lava flow(Qbbk) and in turn is locally covered by the Henrie Knolls lava flow (Qbhk), thusis probably late to middle Pleistocene; however, Johnson and others (2010)suggested that the distal end of the Bowers Knoll flow as mapped here, includingthe part that contains Mammoth Cave, may be the Duck Creek flow―if so,incision there suggests that the Duck Creek flow is about 500,000 years old, farolder than the degree of incision suggests along the upstream part of the flow;maximum exposed thickness is about 15 feet (5 m) near Aspen Mirror Lake, butlikely several tens of feet thick where it fills paleotopography in the Duck Creekdrainage.Qbsk, QbskcStrawberry Knolls lava flows and cinder cones (Pleistocene) – Medium- todark-gray potassic trachybasalt that contains clusters of olivine and clinopyroxenephenocrysts in an aphanitic to fine-grained groundmass; lava flows (Qbsk)erupted from Strawberry Knolls (Qbskc), two cinder cones located about 2 miles(3 km) east of Duck Creek village, and flowed mostly northeast along StrawberryCreek to Uinta Flat; age unknown, but cinder cones are well vegetated and flow isincised by Strawberry Creek as much as 40 feet (12 m) at its downstream end andso is probably middle Pleistocene; lava flows are typically 20 to 30 feet (6-9 m)thick, but doubtless many tens of feet thick near vent areas.Qblhc Lake Hollow cinder cone (Pleistocene) – Forms a small, partly eroded cindercone about 1.5 miles (3 km) north of Mammoth Creek and east of Black RockValley, with a small lava flow (not differentiated on this map) at the base of thecone of medium- to dark-gray hawaiite (sodium-rich trachybasalt) that containsclusters of olivine and clinopyroxene phenocrysts in an aphanitic to fine-grainedgroundmass; vent is on-trend with the Henrie Knolls lava flows, to which it maybe related; age unknown, but likely late to middle Pleistocene based on position inlandscape; lava flow is less than about 20 feet (6 m) thick.Qbef, QbefcEast Fork Deep Creek lava flow and cinder cone (Pleistocene) – Medium- todark-gray, fine-grained olivine basalt lava flow (Qbef) west of Navajo Lake;cinder cone (Qbefc) is deeply eroded due to its location just below the westernescarpment of the Markagunt Plateau, just west of Navajo Lake; the distalsouthern end of this flow was called the Three Creeks lava flow by Biek andHylland (2007), which they estimated to be less than 300,000 years old based ondegree of incision and comparison with nearby dated lava flows; lava flow isprobably 20 to 40 feet (6-12 m) thick.17