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

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Stacked unit depositsStacked unit deposits are used to indicate a discontinuous veneer of Quaternary depositsthat mostly conceal underlying bedrock units. Although most bedrock in the quadrangleis partly covered by colluvium or other surficial deposits, we use stacked units to indicatethose areas where bedrock is almost wholly obscured by surficial deposits that arederived from more than just residual weathering of underlying bedrock.Qlao/Qbmk 3Older lacustrine sediment and alluvium over the Miller Knoll lava flow(Holocene and upper Pleistocene/Holocene to upper Pleistocene) − Mapped alongthe southeast edge of Blue Spring Valley (about 2 miles [3 km] southwest ofPanguitch Lake) where the oldest Miller Knoll lava flow (Qbmk 3 ) is partlyconcealed by a veneer of sediment interpreted to be a mixture of lacustrine andalluvial, and possibly eolian, sand and silt; Blue Spring Valley likely drainedthrough Black Rock Valley prior to being blocked by the Miller Knoll lava flows,with lacustrine and alluvial sediment accumulating in the basin upstream of theflows; surficial cover is likely less than 6 feet (2 m) thick.Qc/TbhColluvium over the Brian Head Formation (Holocene to Pleistocene/Oligoceneto Eocene) – Mapped on the west flank of Houston Mountain (6 miles [10 km]east of Cedar Breaks National Monument) and south of the town of Brian Head,where colluvium, residual deposits, and possibly landslide deposits conceal theunderlying Brian Head Formation; at Houston Mountain, colluvium includes largeblocks of the Houston Mountain lava flow enclosed in a matrix of colluviumderived from weathered, tuffaceous Brian Head strata; surficial cover may exceed20 feet (6 m) thick.Qc/TcwuColluvium over the upper limestone unit of the white member of the ClaronFormation (Holocene and upper Pleistocene/Eocene) – Mapped on the southwestside of Houston Mountain (6 miles [10 km] east of Cedar Breaks NationalMonument) where colluvium conceals the underlying upper limestone unit of thewhite member of the Claron Formation; colluvium includes large blocks of theHouston Mountain lava flow enclosed in a matrix of colluvium derived fromweathered, tuffaceous Brian Head strata and the upper limestone unit of the whitemember of the Claron Formation; surficial cover may exceed 10 feet (3 m) thick.QUATERNARY-TERTIARYHolocene(?) to Late Tertiary lava flowsBasaltic and andesitic lava flows in the Panguitch 30’ x 60’ quadrangle are at thenorthern edge of the Western Grand Canyon basaltic field, which extends across thesouthwest part of the Colorado Plateau and adjacent transition zone with the Basin andRange Province in southwest Utah, northeast Arizona, and adjacent Nevada (Hamblin,1963, 1970, 1987; Best and Brimhall, 1970, 1974; Best and others, 1980; Smith andothers, 1999; Johnson and others, 2010). This volcanic field contains hundreds ofrelatively small-volume, widely scattered, mostly basaltic lava flows and cinder cones11
that range in age from Miocene to Holocene. In southwestern Utah, basalts aresynchronous with basin-range deformation and are part of mostly small, bimodal (basaltand high-silica rhyolite) eruptive centers (Christiansen and Lipman, 1972; Rowley andDixon, 2001). The oldest basalts in southwestern Utah are about 17 Ma (basalt ofHarrison Peak; Biek and others, 2009). The youngest dated lava flow in southwest Utahis the 32,000-year-old Santa Clara basaltic lava flow (Willis and others, 2006; Biek andothers, 2009), but the Miller Knoll, Dry Valley, and Panguitch Lake lava flows south ofPanguitch Lake may be younger still. Red-hot lava flows, an integral part of theSouthern Paiute legend “How the whistler [bird] and badger got their homes,” may relateto the Panguitch Lake-area lava flows (Palmer, 1957; Southern Paiutes lived in southwestUtah beginning about A.D. 1100 [Canaday, 2001]). Schulman (1956) briefly reported on850- to 950-year-old juniper (Juniperus scopulorum) trees growing on young lava flows,thus showing that the lava flows are at least that old but still could be many thousands ofyears old; these lava flows are apparently near Panguitch Lake although definitive samplelocations are unavailable (samples BRY 2104 and BRY 2110, table “Overage droughtconifers,” p. 32). Apart from the mafic block and ash flow that is apparently part of the20 Ma Markagunt megabreccia, the oldest basaltic lava flows in the map area are theHouston Mountain flow (Tbhm), for which we report a new 40 Ar/ 39 Ar plateau age of 5.27± 0.14 Ma, and the 5.3 Ma Dickinson Hill and Rock Canyon flows; Stowell (2006)reported an 40 Ar/ 39 Ar plateau age of 2.78 ± 0.16 Ma for what is likely the Blue SpringMountain lava flow, and an 40 Ar/ 39 Ar maximum isochron age of 0.60 ± 0.25 Ma for whatis likely the Long Flat lava flow.Lava flows in the map area typically have a rubbly base, a dense, jointed middlepart, and – if not eroded away – a vesicular upper part that has a rough aa (a Hawaiianterm for a blocky, jagged flow) or, rarely, a poorly developed pahoehoe (a Hawaiian termfor a smooth or ropy flow) surface. Several lava flows, including the Duck Creek andBowers Knoll lava flows, contain open lava tubes; the best known is Mammoth Cave (6miles [10 km] northeast of Duck Creek Village). The flows commonly overlie streamgraveland other surficial deposits. Older lava flows are partly covered by eolian sandand calcic soil (caliche) not shown on this map. Most lava flows are dark gray and finegrained, and contain small olivine phenocrysts and common crystal clusters of olivine,plagioclase, and clinopyroxene. With few exceptions, these lava flows are difficult todistinguish by hand sample alone. They are distinguished for this geologic map bydetailed geologic mapping, trace-element geochemistry, and radiometric ages.The lava flows in the map area provide a “snapshot” of the local landscape as itexisted when the flow erupted. Each flow was emplaced in a “geological instant” (mostsmall basaltic volcano vents produce only one eruptive cycle that may last less than ayear or as much as a few tens of years in duration), flowed several miles across thelandscape, and is resistant to erosion. Because lava flows blocked drainages, streamswere shunted to the side where they preferentially eroded adjacent, less resistantsedimentary strata, ultimately leaving the resistant lava flows stranded as elevated,sinuous ridges (called inverted valleys) that mark the location of former channels.Southwest Utah is famous for its classic examples of inverted topography, such asWashington and Middleton Black Ridges near St. George, as first described in detail byHamblin (1963, 1970, 1987) and Hamblin and others (1981). Classic, if lesser known,inverted valleys are present on the east-tilted Markagunt Plateau as well, as at the distal12
Page 1 and 2: ! !! !!! ! ! !! ! ! ! !! ! !! !! !
Page 3 and 4: MAP UNIT DESCRIPTIONSQUATERNARYAllu
Page 5 and 6: Qafc Coalesced fan alluvium of Paro
Page 7 and 8: glacial deposits and features that
Page 9 and 10: (Tbhv) and Dakota (Kd and Ktd) Form
Page 11: typically mapped where lava flows d
Page 15 and 16: fronts (except at Dry Valley, immed
Page 17 and 18: the quadrangle; no fault that postd
Page 19 and 20: Qbw, QbwcWater Canyon lava flow and
Page 21 and 22: others, 2007); lava flow is typical
Page 23 and 24: Mahogany Hill, about 500 feet (150
Page 25 and 26: lava flow (Tbbm) that conceal the u
Page 27 and 28: TERTIARYpreserved in down-dropped b
Page 29 and 30: and Rowley and others (in preparati
Page 31 and 32: field (or possibly coeval batholith
Page 33 and 34: hidden by shadow; we tentatively as
Page 35 and 36: esistant crystal-poor rhyolite tuff
Page 37 and 38: thickness uncertain but outcrop pat
Page 39 and 40: divide between Red Creek and Little
Page 41 and 42: pyroxene (5%), and sanidine (trace)
Page 43 and 44: unconformityThe Leach Canyon Format
Page 45 and 46: unconformityMa (Best and others, 19
Page 47 and 48: interval, and a lower limestone int
Page 49 and 50: Figure 3. View northwest to North V
Page 51 and 52: dark-yellowish-orange, grayish-pink
Page 53 and 54: TKgc Grand Castle Formation, undivi
Page 55 and 56: track (the latter found by Eric Rob
Page 57 and 58: noted by Moore and Straub (2001) an
Page 59 and 60: shoreface, beach, lagoonal, and est
Page 61 and 62: water deposits of Cenomanian age (N
Page 63 and 64:
62Figure 7. Cedar Mountain Formatio
Page 65 and 66:
leached white under the Cretaceous
Page 67 and 68:
ACKNOWLEDGMENTSThis geologic map is
Page 69 and 70:
Anderson, R.E., and Christenson, G.
Page 71 and 72:
Biek, R.F., Rowley, P.D., Hayden, J
Page 73 and 74:
field guide (The Mackin Volume): Ut
Page 75 and 76:
2001, Cretaceous and early Tertiary
Page 77 and 78:
Hacker, D.B., Rowley, P.D., Blank,
Page 79 and 80:
Kurlich, R.A., III, 1990, Geology o
Page 81 and 82:
Maldonado, F., and Moore, R.C., 199
Page 83 and 84:
Flagstaff-Green River basins [abs.]
Page 85 and 86:
elation to other igneous centers in
Page 87 and 88:
Schulman, E., 1956, Dendroclimatic
Page 89:
Van Kooten, G.K., 1988, Structure a
Page 92:
113°00'112°00'15BV20R i v e rCCNP
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Interim Geologic Map of the West Part of - Utah Geological Survey

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