SURFICIAL GEOLOGY of the ONEIDA NARROWS AREA, CARIBOU and FRANKLIN COUNTIES, IDAHO HILL THA THA Pgs

IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 12-6 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG COOLEY AND PEDERSON

1:24,000 Scale REFERENCES Quadrangle, southeastern ID, U.S. Geological Survey calibrated using Lava Creek B tephra, Geology 29, p. Anderson, S.A., 1998, Sedimentology, hydrology, and Miscellaneous Investigations Map, 1:24,000 scale 783-786 sequence stratigraphy of Pleistocene Bear River delta, Armstrong, R.L.; Leeman, W.P.; Malde, H.E., 1975, K-Ar Fiesinger, D.W.; Perkins, W.D.; Puchy, B.J., 1982, TCHER TCHER Cache Valley, ID, MS Thesis, Idaho State University, 61 dating, Quaternary and Neogene volcanic rocks of the Mineralogy and petrology of Tertiary-Quaternary SURFICIAL GEOLOGY OF THE ONEIDA NARROWS AREA, CARIBOU AND FRANKLIN COUNTIES, IDAHO HILL THA THA pgs. Snake River Plain, ID, Journal of Science 275, p. 225- volcanic rocks in Caribou County, ID, in Bonnichsen, B.; Anderson, S.A.; Link, P.K., 1998, Lake Bonneville 251 Breckenridge, R.M. (editors), Cenozoic Geology of ON sequence stratigraphy, Pleistocene Bear River delta, Bouchard, D.P., 1997, Quaternary Bear River Idaho, Idaho Bureau of Mines and Geology Bulletin 26, Skye W. Cooley and Joel L. Pederson Cache Valley, ID, in Pitman, J.K.; Carroll, A.R. paleohydrogeography reconstructed from 87Sr/86Sr p. 465-488 IDAHO ONEIDA RES. composition of lacustrine fossils, MS Thesis, Utah State Gilbert, G.K., 1890, Lake Bonneville, U.S. Geological Utah State University, Department of Geology, Logan UT NARROWS (editors), Modern and Ancient Lake Systems, TREASURET Utah Geological Association Guidebook University, 92 pgs. Survey Monograph 1, 438 pgs. Bouchard D.P.; Kaufman D.S.; Hochberg, A.; Quade J., Hochberg, A., 1997, Aminostratigraphy of Thatcher Basin, LAKE BONNEVILLE SEDIMENTS (PLEISTOCENE) - Poorly- QUADRANGLE 26, p. 91-104 DESCRIPTION OF MAP UNITS Qbo FUNDING 1998, Quaternary history of the Thatcher Basin, ID, southeast ID: Reassessment of Pleistocene lakes, MS 2012 consolidated, stratified, light red to pink to white sand, silt, U.S. Geological Survey National Cooperative Mapping LOCATION Armstrong, R.L.; Oriel, S.S., 1965, and minor gravel in thin, repetitious, flat-lying and oscillation- MINK reconstructed from the 87Sr/86Sr and amino acid Thesis, Utah State University, 112 pgs. ALLUVIUM (HOLOCENE) - Well to poorly sorted gravel, Program, Colorado Scientific Society William G. Pierce Grant, CREEK Tectonic development of the Qa Map A RIVERDALE composition of lacustrine fossils: Implications for the Izett, G., 1981, Stratigraphic succession, isotopic ages, sand, silt, and interbedded clay in floodplain of the modern and climbing-ripple beds deposited upstream and inside Tobacco Root Geological Society, Utah State University Idaho-Wyoming thrust belt, Oneida Narrows gorge during Bonneville highstand at ~20 ka AAPG Bulletin 49, p. 1847- diversion of the Bear River into the Bonneville Basin, partial chemical analyses, and sources of certain silicic Bear River. Clasts are rounded brown, purple, pink, and white Graduate Senate Travel Fund, Cirque Geoscience Consultants, ADJOINING Qgv fine- to coarse-grained quartzite cobbles derived from the (Oviatt and Miller, 1997). Red color is from hematitic 1866 Palaeogeography, Palaeoclimatology, Palaeoecology volcanic ash beds (4.0-0.1 m.y.) of the western United GEOLOGY BACKGROUND and Wildlife Demographics. er QUADRANGLES Neoproterozoic to Cambrian Brigham Group and Cambrian Mesozoic shales in valley fill deposits of thrust belt basins v Armstrong, F.C., 1969, 141, p. 95-114 States, U.S. Geological Survey Open File Report 81-763, Quaternary deposits on this 1:24,000-scale map were mapped in carbonate units. Floodplain deposits are reworked Tertiary and traversed by the Bear River. Locally gypsiferous near seeps. ACKNOWLEDGMENTS Ri Geologic Map of Bright, R.C., 1960, Geology of the Cleveland area, 2 sheets 2009 by S.W. Cooley. Mapping covers portions of six 7.5' Pleistocene valley fill deposits and Gem Valley Basalts. Unit Relatively thin deposit (5-20m thick) forms low, dissected 111 45' 00" the Soda southeastern ID, MS Thesis, University of Utah, 262 pgs. Kaufman, D.S., 2003, Amino acid paleothermometry of Thanks Ross Smith, Treasure Valley Cement Company, MX Qmc quadrangles including Thatcher Hill, Thatcher, Treasureton, Oneida covers most of the broad valley flood in Mound and Gentile benches at 1555m (5100ft) below the basalt rim in Gentile Springs Bright, R.C., 1963, Pleistocene Lakes Thatcher and Quaternary ostracodes from the Bonneville Basin, UT, Ranch, and the landowners of Gem, Gentile, and Mound Bonneville, southeastern ID, PhD Dissertation, Quaternary Science Reviews 22, p. 899-914 Narrows Reservoir, Riverdale, and Mink Creek. The work builds on Valleys and includes the area subject to inundation by the 1- Valley. Valleys for access to their property, IGS Research Geologist University of Minnesota, 292 pgs. Keller, A.S., 1952, Geology of the Mink Creek region, ID, previous mapping by Bright (1960, 1963, 1967) and Oriel and percent-annual-chance floods (FEMA Zone A). It is Bill Phillips for enthusiastic discussions in the field and characterized by well-drained soils and productive agriculture Qlbr BEAR RIVER DELTA (PLEISTOCENE) - Poorly-consolidated, Bright, R.C., 1967, Late Pleistocene stratigraphy in Thatcher MS Thesis, University of Utah Platt (1980). The map depicts alluvium, colluvium, eolian, and stratified, light red to pink to white sand, silt, and minor gravel cartographic review, Professor Don Fiesinger for information Basin, southeastern ID, Tebiwa 10, p. 1-7 Lanphere, M.A.; Champion, D.E.; Christiansen, R.L; Izett, mass wasting deposits where they occur in mappable units. Unit ground. Mapped as Qls, Qlg, Qll in Cache Valley (Williams, on the Gem Valley Basalts, University of Minnesota Emeritus 1942). deposited downstream of Oneida Narrows gorge during Lake Bright, R.C.; Ore, H.T., 1987, Evidence for the spillover of G.A.; Obradovich, J.D., 2002, Revised ages for tuffs of descriptions were modified from mapping by the above authors Bonneville highstand at ~20ka. Exposed thickness is 110m Professor Herb E. Wright (Bright's PhD advisor) for discussions Lake Bonneville, southeastern ID, in Bues, S. (editor), the Yellowstone Plateau volcanic field; assignment of the of Bright's work, Preston HS Librarian Janelle Butters for Oneida and Gilbert (1890), Danzl (1982), Bright and Ore (1987), LANDSLIDE DEPOSITS (PLEISTOCENE and HOLOCENE) - (360ft). Repeated architectural elements include prodelta silt GSA Centennial Field Guide 2: Rocky Mountain Huckleberry Ridge Tuff to a new geomagnetic polarity Qms memories of Robert C. Bright, graduate student Joshua Keeley, Narrows Qbo Hochberg (1996), Anderson (1998), Bouchard et al. (1998), Link et Unconsolidated, poorly sorted, clast- and matrix-supported and clay (1-7m), delta front gravity flows with sand-clay Qmc Section, p. 143-146 event, GSA Bulletin 114, p. 559-568 Professor Dave Rodgers, and Professor Paul Link of Idaho State Reservoir al. (1999), Carney et al. (2003), and Steely and Janecke (2005). pebble to boulder conglomerate and diamict. Above highest couplets (0.5-10m thick), and delta top channel sands (0.5- Qmc Bright, R.C.; Rubin, M., 1965, Part H: Lake Bonneville, in Link, P.K., Kaufman, D.S.; Thackray, G.D., 1999, Field guide University Geosciences Department for mapping Lake Thatcher shoreline (1660m, 5445'), occurs in arcuate, 23m thick), and strath terrace gravels inset into other facies Qgv Schultz, C.B.; Smith, H.T.U. (editors), 7th INQUA to Pleistocene Lakes Thatcher and Bonneville and the collaboration and helpful reviews of an early draft, Professor Map B LAKE THATCHER & MAIN CANYON FORMATION vegetated scarps and slumps. Below, as steep escarpments (Anderson & Link, 1998). Red color is from hematitic Congress, Guidebook E: Northern and Middle Bonneville Flood, southeastern ID, in Hughes, S.S.; Barbara Nash of University of Utah Geology & Geophysics The map covers most of the area occupied by Pleistocene Lake usually along the Bear River. A few large slides are present Mesozoic shales. Forms unstable bluffs along Bear River Rocky Mountains, p. 104-112 Thackray, G.D. (editors), Guidebook to the Geology of Department for ash correlation. Thatcher (Bright, 1967). Deposits associated with the ~200 km2 beneath steep, bedrock cliffs near Oneida Narrows Dam. between Mink Creek and Preston. Danzl, R.B., 1982, Stratigraphy and Eastern Idaho, Idaho Museum of Natural History, p. 251- lake are known today as the Main Canyon Formation (Qmc). The depositional environment of the Tertiary 266 ALLUVIAL TOESLOPES & FANS (HOLOCENE) - Reworked MAIN CANYON FORMATION (PLEISTOCENE) - Poorly- to Qbo Qgv former lake basin is divided into three sections on topographic Qf Qmc Salt Lake Group near Oneida Link, P.K.; Mahoney, J.B.; McCalpin, J.; Henkelman, J.J.; silt, sand, and gravel derived from units that lie immediately moderately-well consolidated light-gray, tan, yellow, white, Narrows, southeastern ID, Smith, B.L., 1987, Field trip roadlog for the Bear River maps: Gem, Gentile, and Mound Valleys. Gem Valley extends Qf Qmc upslope. Unit forms low-relief, fans and aprons below terrace brown, and light-green silt, sand, and marl deposited on the Northwest Geology, 11, p. 22- Landslide Complex, Proceedings of the 23rd Symposium from approximately Soda Springs gap near Alexander, ID escarpments. floor and margin of Lake Thatcher (2Ma to ~50ka, Bright, Qm 30 on Engineering Geology and Soils Engineering, p. 334- southward to the edge of the basalt escarpment near Niter, ID. 1967; Bouchard et al., 1998). Unit interfingers with Gem Bear Dethier, D.P., 2001, 353 TRAVERTINE & TUFA (PLEISTOCENE and HOLOCENE) - Map C Gentile Valley extends from the basalt escarpment to the mouth of Qtt Valley Basalts and pediment deposits (QTp) and alluvial fans R 40 E Pleistocene incision Malde, H.E., 1968, The catastrophic Late Pleistocene Porous, gray to white to yellowish-gray calcium carbonate Qf Trout Creek. Mound Valley extends from Trout Creek to the upper (Qaf). Prominent shoreline bench at 1660m (5445ft). Exposed rates in the Bonneville Flood in the Snake River Plain, ID, U.S. hotspring (travertine, dense, banded) and warmspring (tufa, Qmc end of Oneida Narrows gorge. thickness estimate of 320m (1050ft) by Bright (1963), but well Qm western United Geological Survey Professional Paper, 596, 73 pgs. porous) deposits that form low mounds, cones, and round- logs indicate it may be 600m (1970ft) thick. Numerous small, R 41 E States Malde, H.E.; Trimble, D.E., 1965, Malad Springs to topped benches (up to 40m thick) along the flanks of Mound, Lake Thatcher existed from ~2Ma to ~50ka. From approximately active landslides. This Technical Report is a reproduction of independent Qf Pocatello, in Schultz, C.B.; Smith, H.T.U. (editors), 7th Gentile, and Gem Valleys between 1525-1615m (5000- Qm 700ka to ~50ka, Thatcher basin functioned as a receiving basin mapping by Skye W. Cooley and Joel L. Pederson at Utah INQUA Congress, Guidebook E: Northern and Middle 5300ft) elevation, probably atop faults. Unit includes both BASIN FILL BOULDER GRAVELS (PLEISTOCENE) - Boulder, Qmc and sediment trap for local streams draining adjacent the Qg State University. Its content and format may not conform Qmc Rocky Mountains, p. 98-103 remnant and actively-forming deposits with flowing springs, cobble, and coarse gravel of Bull Lake(?) age valley fill. Qmc mountains. The lake filled a structural depression formed during to agency standards. Mansfield, G.R., 1927, Geography, geology and mineral many developed for irrigation. These relatively resistant Reworked locally and may interfinger with QTp. resources of southeastern Idaho, U.S. Geological Late Miocene to Pleistocene Basin and Range extension (Janecke geothermal spring deposits confine the modern Bear River ALLUVIAL FAN - PEDIMENT SURFACE (MIOCENE- Qmc Survey Professional Paper 152, 453 pgs. et al., 2003). Today, the Bear River flows through the valley, joined channel in places, pose obstacles to cultivation, are QTp Qbo Qbo Qf O'Connor, J.E., 1993, Hydrology, hydraulics, and by several tributaries headed in the Bear River Range and Fish developed for recreation, and the hold potential for PLEISTOCENE) - High elevation, low-relief pediment surface Qm geomorphology of the Bonneville flood, GSA Creek Range. Thatcher's northern shoreline corresponded with a aquaculture or specialty greenhouse crops. Mapped as Qt Special Paper 274, 83 pgs. prominent basalt flow-front escarpment (Mansfield, 1927; Oriel (Oriel and Platt, 1968; Armstrong, 1969), Qpt (Bright, 1960), Ore, H.T., 1999, in Link, P.K., Kaufman, D.S.; Qt (Bright, 1963), and Qlt in Cache Valley (Williams, 1962). and Platt, 1980; Bright, 1963). The southern shoreline was the Qmc Thackray, G.D., 1999, Field guide to Pleistocene flanks of the Bear River Range and Oneida Narrows gorge. PROVO LEVEL TERRACE GRAVELS (PLEISTOCENE) - River Qmc Lakes Thatcher and Bonneville and the Stratigraphic sections (Hochbergh, 1997; Bouchard, 1997) indicate Qagt4 Qm Qa gravels capping a prominent inset terrace (1445m, 4740ft) of Bonneville Flood, southeastern ID, in Hughes, lake level fluctuated through time. A discontinuous bench marking the paleo-Bear River following the 14.5ka Bonneville Qc S.S.; Thackray, G.D. (editors), Guidebook to the the lake's highstand level is visible today at 1660m (5446') (Bright, Flood. Qa Geology of Eastern Idaho, Idaho Museum of 1963). Qagt4 Natural History, p. 254-255 Qagt3 QTp QTp TERRACE GRAVELS (PLEISTOCENE) - River gravels Qagt3 Oriel, S.S.; Platt, L.B., 1980, Geologic Map of the The Main Canyon Formation is stratigraphically divided into upper Qagt1 capping an unnamed, discontinuous, terrace of Map Area B Qa Preston 1x2 degree Quadrangle, ID and WY, U.S. (deep lake) and lower (shallow lake) sections (Bouchard et al., the paleo-Bear River located below the Provo Qbo Geological Survey Miscellaneous Investigations 1998). The type section, largely obscured today, is located in the Level. Series Map I-1127, p. 1:250,000 scale Kuntz Creek drainage along the Main Canyon Dugway canal. A Map Area A Qmc Oviatt, C.G., 1997, Lake Bonneville fluctuations and number of other exposures are found Approximately 200m of global climate change, Geology, 25, p. 155-158 section are exposed in roadcuts, escarpments, and cutbanks in the Peale, A.C., 1879, Chapter IV: Descriptive geology - map area. Well logs indicate a total thickness of the MCF is 600m. Qbo Snake River drainage; Chapter V: Bear River drainage; Chapter VI: Resume of the The lower section contains the 2Ma Lava Creek B, the 640ka Qlbr Qagt3 Qf Qmc geographical formations of the district, in Huckleberry Ridge, the 150ka Hebgen Narrows (Izett, 1981; R 39 E R 40 E Qf Qagt4 Qf Qa Hayden, F.V., 11th Annual Report of the U.S. Sarna-Wojcicki et al., 1984; Lanphere et al., 2002). The upper Qg Qagt1 Qlbr Qgv Geological Survey of The Territories, ID and WY section contains a ~110ka Mt. St. Helens, possibly that of Berger Qlbr MAP SYMBOLS Qf Qm 1877, p. 543-646 and Busacca (1995). A 2.5m-thick slug of white ash located in a Qm Qlbr Qg Perkins, M.E.; Nash, B.P., 2002, Explosive silicic brushy escarpment below a canal near Thatcher, ID (T11S, R40E, Contact volcanism of the Yellowstone hotspot: The ash- fall tuff record, GSA Bulletin 114, p. 367-381 SW 15, ~1510m elevation), was first sampled by Izett (1981, Qagt4 Qagt1 Qm AH94-x) and identified as Huckleberry Ridge, later resampled by Qf Active Channel Boundary (Apprx.) Puchy, B.J., 1981, Mineralogy and petrology of lava A. Hochberg, and tentatively confirmed by W. Nash at University flows (Tertiary-Quaternary) in southeastern ID of Utah (unpublished lab report, 1995). The flat-lying ash is and Black Mountain, Rich County, UT, MS Qa Onieda Thesis, Utah State University, 73 pgs. contained within(?) a slump block. Flame structures are present Qf Qagt4 Qf Qf Treasureton Narrows Sarna-Wojicicki, A.M.,1984, Chemical analyses near its base. The lower contact is not exposed. Reservoir Qf correlations, and ages of Upper Pliocene and Qagt4 Qbo ONEIDA NARROWS GORGE Qlbr 111 45' 00" Pleistocene ash layers of east central and southern CA, U.S. Geological Survey The cutting of the 275m-deep Oneida Narrows gorge by the Bear Qbo Qf Professional Paper 1293 River is thought to have occurred in (Malde and Trimble, 1965). Qagt1 Qa Qagt1 Qa Qf Smith, N.J., 1953, Tertiary stratigraphy of northern The first cutting event is poorly understood, but believed to have Qagt4 strath Qc Qf UT and southeastern ID, 4th Field Qm occured during the Miocene (Ore, 1999). Increased sedimentation Qagt4 Qlbr Conference of the Intermountain Qmc during the Bull Lake glaciation (~140ka) may have led to Qagt3 Association of Petroleum Qmc backfilling of the gorge, which was subsequently excavated to its Qagt4 T 11 S Geologists, p. 73-77 present day configuration at ~50ka when the formerly north- T 11 S Steely, A.N.; Janecke, S.U.; Long, S.P.; Qlbr Qm T 12 S Qagt1 Carney, S.C.; Oaks, R.Q.; flowing Bear River was redirected south into the Bonneville Basin T 12 S Qf Qlbr Map Area C Langenheim, V.E.; Link, P.K., 2005, by basalt eruptions in Gem Valley. Thick basin fill gravels at the Qlbr Qagt2 Evolution of a Late Cenozoic mouths of Cottonwood, Ant, and Williams, and Mink Creeks hint Qgv at depth of the Bull Lake(?) fill since removed from the gorge. Qf Qbo supradetachment basin above a flat-on-flat detachment with a folded lateral ramp, Gravel pits and natural escarpments along Cottonwood Creek exposed along Qagt1 Qf QTp southeast ID, in Pederson, J.l.; Dehler, C.M. between Cleveland and the McGregor Bridge expose fluvially- the flanks of the Fish Creek Range and Bear Qmc Qgv Qmc Qmc (editors), Interior Western United States, GSA reworked fill gravels that interfinger with Qbo. An OSL age of Qagt3 Fill Qmc River Range generally strath Qm Field Guide 6, p. 169-198 ~20ka on the gravel (unpublished data by J. Pederson and T. Qa above 1660m (5445ft) QTp Qbo Qmc Williams, J.S.,1962, Lake Bonneville: Geology of Rittenour, 2007) is consistent with <50ka radiocarbon ages of Qlbr southern Cache Valley, UT, U.S. Geological composed of pebble to boulder Qg Qm pluvial Late Pleistocene gorge incision (McCoy, 1997; Bouchard et deposits, coalesced fans Qm Survey Professional Paper 257-C, 152 Qg al., 1998; Kaufman, 2003). This latest incision may correspond to (rounded, poorly-sorted, clast- Qgv Qa pgs. increased erosion driven by the Late Pleistocene pluvial climate. Qlbr supported, cobble to boulder Qlbr Wilson, J.R., 1992, Field Guide to The gorge was open to Thatcher Basin prior to 20ka, when Lake conglomerate with clasts of quartzite Geologic Excursions in Utah strath Bonneville expanded to its highstand lake level; red lacustrine Qagt4 derived from Brigham Group, Paleozoic QTp Qmc and Adjacent Areas of NV, deposits (Qbo) partially fill limestone caves inside Oneida Narrows limestones and dolostones from Cambrian Qg Qm ID and WY: GSA Rocky Qagt1 Mountain Section/Utah and the floor of Thatcher basin. Gorge cutting and reestablishment carbonates, and shale chips from the Tertiary Salt Qm Qbo Geological Survey, of the river 150m (490ft) lower at the level of Lake Bonneville prior Qf Lake Fm), hillslope colluvium (<10m thick), and loess. Fans show inter-tonging relationships with fine- 481 pgs. to 20ka and catastrophic flooding (14.5ka) resulted in rapid Qa Qf Qlbr grained Qmc and with Qgv in water well logs. Unit is excavation of Tertiary to Pleistocene valley fill sediments (i.e., interpreted as pediment atop basin fill eroded from Cenozoic Qm Qc Qa Dethier, 2001) by the Bear River and its tributaries in Thatcher Qlbr block uplifts, locally reworked by Pleistocene streams. The Qmc basin and northern Cache Valley. basinward-sloping pediment surface is generally planar, Qg R locally tilted, truncates tilted Tertiary bedrock, and is deeply Qg Oneida Gorge QTp BEAR RIVER DELTA T 14 S incised by the Bear River and its tributaries of the Bear River. Reddish, laminated, fine grained deposits of the Bear River delta QTp T 15 S Bedrock straths with pavements and thin, residual soils are Qaf are well exposed in bluffs at Riverside, ID (Smith, 1953; present locally. The surface is probably correlative with Qg R 39 E R 40 E Qc Anderson, 1997; Anderson & Link, 1998) and along River Road 100,00-200,000 year old McKenzie Flat surface (Southard and QTp Qbo Qbo Qmc in Gentile Valley. Deltaic deposits indicate Oneida gorge was open Williams, 1970; McCalpin, 1989; Oaks et al., 1999), boulder Qm Qagt1 and the Bear River was present in the Bonneville basin during gravels (Bues, 1958), and similar pediments in Cache Valley (Mansfield, 1927; Williams, 1942; Hanson, 1949; Williams et transgression of the lake to its late Pleistocene highstand just prior TERRACE GRAVELS (PLEISTOCENE) - River gravels capping Qagt2 al., 1961, 1962; Gray, 1975; Sprinkel, 1976; Robertson, 1978; 42 15' 00" the catastrophic Bonneville flood at 14.5ka. Delta size and an unnamed, discontinuous, low terrace of the paleo-Bear Qm Qmc thickness (>110m, 360ft) suggest the river was heavily-laden with Garr, 1988). Unit is overlain by Pleistocene-Holocene loess. Qa Qaf River. Modern sediment and flowed into the lake for a significant period of time. SALT LAKE GROUP, UNDIFFERENTIATED (MIOCENE- TERRACE GRAVELS (PLEISTOCENE-HOLOCENE) - River Tsl Bear River Link et al., 1999 note a paucity of coarse grained facies in the Qagt1 PLIOCENE) - Mostly uconsolidated, matrix- to clast-supported, Qm Qa gravels and fine grained floodplain deposits of the Bear River. Riverside bluffs. Except for local deltas of Cottonwood Creek, cobble to boulder conglomerate with matrix of red clay, Qm Qmc Qf Unit spans much of the valley flood and includes oxbow Qc Qg Qf Williams Creeks, and a branch of Trout Creek near South Ant brown silt, and sand. Clasts include rounded, medium-gray Qa ponds an associated wetlands periodically inundated by Cambrian limestones, rounded white, pink, brown, purple QTp Qm Canyon, we found no significant quantities of Bear River gravel floods from the modern channel. Well-drained and productive quartzites derived from the Neoproterozoic to Cambrian T 13 S Qmc upstream of Oneida Narrows. We did, however, map extensive agricultural ground in most areas. Qmc Brigham Group, rare purple slate chips (Brigham Group), and terrace-capping gravels (Qagt units) and cobble deposits (Qg) Qc T 14 S Qg light-gray tuffs. The formation is composed of a basal Cambrian Qbo in 42 22' 30" within and at the downstream outlet of the gorge. Massive slope COLLUVIUM (HOLOCENE and PLEISTOCENE) - Angular, Qagt1 ThatcherHill Thatcher Qbo Qc conglomerate, a medial tuffaceous unit (Cache Valley Fm), Noonan & Qa limestone failures of the 1983 Bear River Landslide Complex are pebble- to boulder-sized quartzite, carbonate, and tuff clasts 42 22' 30" and an upper conglomerate (Mink Creek Fm). Unconformably Qm Bloomington Fms caves Qaf with poorly-developed soils in talus cones, scree aprons, and Qg ws documented in Link et al. (1987) and Link et al., (1999). Wave- oir Qtt debris fans within and below steep, bedrock gullies and at the overlies lower Paleozoic limestones (Cambrian Bloomington, Qagt1 Oneida v dominated deltaic deposits form a huge, low-gradient fan with an Narro base of cliffs inside Oneida Narrows Nounan Fm. Maximum thickness is 2000m (6560ft). reasureton Qmc undulating, dissected topset surface that slopes westward from Qa T Reser Qa 1585-1432m (5200-4700ft) between Mink Creek and the Oxford- GEM VALLEY BASALT (PLEISTOCENE) - Dark gray, fine- to Qgv CARTOGRAPHIC INFORMATION Twin Lakes Reservoir area. Twenty-one back-stepping, millennial- medium-grained, vesicular, porphrytic basalt flows that form 111 45' 00" Base topography (1:24,000 scale USGS DRGs) available from Qm QTp scale parasequences that record the rise of Lake Bonneville are broad, flat to undulating surfaces and local pillows, sinuous Inside Idaho GIS (http://insideidaho.org) and National Bull Lake-age exposed at Riverdale Bluffs (Anderson, 1997; Link et al., 1999). pressure ridges, dome-shaped blisters, cinder cones, lava tube Elevation Dataset (http://ned.usgs.gov). Field work conducted basin fill (?) Parasequences consist of very delta front gravity-flow sheet sands "ice caves", and blocky flow front escarpments. Surfaces of by S.W. Cooley, 2009. Digital cartography by S.W. Cooley, Qf Qbo (prograding), delta top channel sands, and lacustrine silts and clays flows are commonly blanketed by eolian deposits. Unit 2010. PDF of this map available online from Idaho Geological 111 45' 00" Qbo (flooding). Strath terrace gravels (described below) are inset into named by Bright (1967) and mapped as Qpb. Up to a meter Survey (www.idahogeology.org). Qf R of water-worked (sheetflood?), horizontally-bedded, basaltic the unit. lapilli and ash overlies vesicular basalts near Grace Power Map version 1.0 Qg Qal INSET TERRACES Plant. An approximate age of 600ka has been established Qaf (Armstrong et al., 1975), but at least one younger flow, at Several gravel capped terraces (Qagt1-4), inset into Bear River Qa Thatcher, is inset into older flows. A few hundred water wells Qa R delta deposits (Qlbr) near Riverside, record stages of downcutting produce from several zones in the basalt in Gem, Gentile, by the Bear River following the flood-draining of Bonneville Basin and Mound Valleys. Qf at 14.5ka (Malde, 1968; O'Connor, 1993). CORRELATION OF MAP UNITS Qbo Qf Qa Qg Mass Qa Movement Colluvial Cinder Cones Qm Qmc contains clasts Alluvial Deposits Deposits Deposits Bedrock Units Niter of Qmc Loess Qaf Qf Qa Qc Holocene Qtt Paleo-Bear River(?) Flow 3 Qms Qagt1 Qag1 Qag1 Fluvial Gravels Qmc Qf Qagt2 Qag2 R Qagt3 Qbgv QUATERNARY Qbo Qbo Qmc Qagt4 Qg Gentile-Mound Valley Qmc Pleistocene Qbo Qlbr Qmc Qg Qm

QTp Qmc Qg GEM VALLEY BASALTS CENOZOIC Qbo Flow 2 QTp QTp (Qgv) Pliocene Qa Modern Qtt Qag2 Bear River Qbo Qf Tsl Qg Flow 1 TERTIARY Qag2 Qtt Qaf Miocene Qg Qag1 Qa Qm Qag1 Qm Qa Neoproterozoic-Cambrian Brigham Group Qag2 Qg Qmc Cambrian Carbonates Qa Qbo Tertiary Qa Qm Qtt Tertiary Salt Lake Formation Qa T 12 S Basin Fill T 12 S Alluvial Fans Qag2 T 13 S T 13 S Qg Qmc Qmc QTp Qg Qc

R 40 E R 41 E

Niter Loess MN Pressure GEM VALLEY BASALTS Blisters GN (Qgv) o o Riverside Area Gentile Valley 0 40 20 Bear River Delta Modern (Qlbr) Bear River Paleo-Bear River

UTM Grid and Provo Level 1963 Magnetic North Terrace Qf Declination at Center of Map Riverside Paleo-Bear (Qagt4) Landslide River Terrace Qm Complex (Qagt3) Qbo SCALE 1:27,900 (Qm) Modern 1 0.5 0 1 Bear River MILE Qagt2 Qtt Qmc FEET Qf Qtt Qmc 1000 0 1000 2000 3000 4000 5000 6000 7000 KILOMETER Qa Qa 1 0.5 0 1 Tertiary Contour interval 40 feet Salt Lake Neoproterozoic-Cambrian Brigham Group, Fm Cambrian Carbonates,Tertiary Salt Lake Formation

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