IDAHO GEOLOGICAL SURVEY DIGITAL WEB MAP 72 MOSCOW-BOISE-POCATELLO BRECKENRIDGE AND OTHBERG

S URFICIAL G EOLOGIC M AP OF THE C ASCADE Q UADRANGLE, VALLEY C OUNTY, I DAHO

Disclaimer: This Digital Web Map is an informal report and may be Roy M. Breckenridge and Kurt L. Othberg revised and formally published at a later time. Its content and format may not conform to agency standards.

2006 Mapping and data are incorporated in and superseded by DWM-68, Surficial Geologic Map of Long Valley, Valley County, Idaho , 1:50,000 scale.

INTRODUCTION

Qal Long Valley is bounded on the west by the West Mountains, a block of tilted Qobs Qop Columbia River basalt, and on the east by the Salmon River Mountains of Qop Qac Qcg the Idaho batholith. The valley floor is about 4800 feet in elevation and the Qops adjacent glaciated mountains rise above 7000 feet. The Payette Lakes are Qop dammed behind a sequence of Pleistocene end moraines and Tertiary basalt Qops is exposed along the shorelines. The geology of this part of Long Valley is dominated by valley alluvium and mountain-slope colluvium.

The placer deposits of Long Valley were studied in the 1950s by D.L. Schmidt and J.H. Mackin. Geology depicted on this 1:24,000-scale Cascade 7.5' Qal quadrangle is based partly on their mapping (Schmidt and Mackin, 1970). Qops Colman and Pierce (1981, 1983) used weathering-rind dating techniques Qal Qac to subdivide the glacial sequence and estimate the numerical ages of Schmidt and Mackin’s units but did not map the quadrangle. The landforms and Qop surface deposits of the area were described by Othberg (1987). This map Qcg subdivides the glacial stratigraphy based on genesis, geomorphology, texture and relative age of the surficial units. The map uses terminology of Schmidt Qac and Mackin (1970) and the Rocky Mountain Glacial model (Mears, 1974), not because the units are directly correlated to the type localities, but because Qas of the informal relationship to equivalent units in Idaho.

DESCRIPTION OF MAP UNITS

Qop Qac MAN-MADE DEPOSITS Qop Qcg m Made land (historic)—Mixed deposits of man-made fill. Mostly coarse-grained ballast and sandy fill from local sources. Made land includes highway and Qal railroad beds, landfills, constructed levees, and earth-fill dams. ? LAKE DEPOSITS Qops Qb Beach deposits (historic)—Coarse sand to silty sand. Forms newly accreted beaches, bars, and spits in areas of lower wave energy along the shore of ? Cascade Reservoir. Thickness less than 10 feet. Qb Qcg Qal Qcg Qac Qac Qas ALLUVIAL DEPOSITS Qac Qal Alluvium of the North Fork Payette River (historic and late Holocene)—Stratified ? Qas Qal pebbly sand in channel bars and islands. Stratified silt, clay, and sand in Qac Qb Qcg abandoned channels. Continuously to seasonally saturated; has potential ? ? Qas for flooding. Soils primarily Blackwell, Jurvannah, Kangas, and Melton series (Rasmussen, 1981). In north part of map submerged in Cascade Reservoir. m Qac Thickness more than 20 feet.

Older alluvium of the North Fork Payette River (Holocene)—Primarily Stratified Qb Qac Qas Qalo m sand of pre-modern channel and flood-plain deposits. Forms low terrace Qac Qcg with river-cut edge. Soils primarily Donnel and Roseberry series (Rasmussen, 1981). Thickness more than 20 feet.

Qas3 Qac Alluvium of the Beaver and Pearsol Creek drainages, which are graded to the North Fork Payette River.

Qas Alluvium of side streams (historic and late Holocene)—Stratified silt, clay, m 1 and silty sand. Buries sand of older terrace alluvium. Typically confined to narrow drainageways that are incised into older alluvium. Seasonally saturated Qas and has potential for flooding. Soils primarily Blackwell, Cabarton, and m Melton series (Rasmussen, 1981). Thickness 2-10 feet. m Qcg Qb Qas2 Alluvium of lower side-stream terraces (late Pleistocene)—Stratified fine to coarse sand. Forms broad terrace east and north of Cascade. Steam-cut Qac terrace scarp bordered by meanders and meander scars of North Fork of Payette River. Terrace surface somewhat dissected and is seasonally saturated Qcg Qb in lower topographic positions. Soils primarily Donnel and Roseberry series (Rasmussen, 1981). Thickness more than 10 feet.

Qas3 Alluvium of higher side-stream terraces (pre-late Pleistocene)—Silty, clayey Qb sand grading downward into stratified medium to coarse sand. Forms dissected Qb terrace characterized by low undulating topography. Edge of terrace is diffuse and irregular owing to local erosion graded to younger stream systems. Soil Qac primarily Archabal series (Rasmussen, 1981). Thickness more than 10 feet.

Qas3 Qas Alluvium of side streams, undivided (historic, Holocene, and Pleistocene)— Variable clayey silt, silty sand, coarse sand, and pebbly sand form narrow Qb m channels, flood plains, and low terraces in stream valleys and plains graded Qac to the former course of North Fork Payette River, to Cascade Reservoir, and to Jemima K Reservoir. Soils primarily Archabal, Blackwell, Gestrin, and Qb Qcg Melton series (Rasmussen, 1981). Thickness 2 feet to more than 10 feet.

Qac Qaf Alluvial-fan deposits (Holocene)—Silty sand, coarse sand, and gravelly sand. Stratified to crudely bedded. Forms low-relief fans at mouths of steep, narrow Qac Qas1 valleys draining the east side of Crown Point. Has potential for flooding during snow melt or thunderstorms. Thickness 2-20 feet.

Qas3 Qac Qac Alluvium and colluvium (Holocene and Pleistocene)—Silty sand to pebbly Qac coarse sand. Poorly stratified to massive. Forms fans and aprons in foot slopes Qas3 and gently sloping granitic colluvial slopes. Locally includes old erosion Qb m surfaces, lag deposits, and tors. Soils primarily Archabal, Gestrin, Shellrock, and Takeuchi series (Rasmussen, 1981). Thickness 2-20 feet.

GLACIAL AND RELATED DEPOSITS Qb Qdf Debris-fan deposits (Pleistocene)—Pebbles, cobbles, and boulders in a silty m Qac sand matrix. Poorly to crudely sorted; angular to subrounded clasts of basalt Qas1 and granitic rocks. Debris flows and alluvium derived from steep slopes

Qb Qas2 where complex glacial and periglacial processes interact. Soils include m McCall and Nisula series (Rasmussen, 1981). Thickness 5-50 feet. Qb m Qas 3 Qta Alpine till deposits, undivided (Holocene and late Pleistocene)—Brown to gray

Qas2 silty, sandy cobble- to boulder till and protalus. Predominantly unsorted and unstratified. Mostly restricted to alpine cirques above 6000 feet elevation.. Qos Soils primarily Byron and Pyle series (Rasmussen, 1981). Thickness 5-30 feet.

Qas1 Scattered deposits till, undivided (Pleistocene)—Mostly brown to gray silty, Qts Qts Qcg sandy gravel. Gravel is pebble-to boulder-sized clasts of basalt and granitic rocks. Extent of till is discontinuous in steep-mountain bedrock terrain. Qb Qcg Qdf m Common bedrock outcrop. Density of clast pattern on map indicates relative Qaf distribution and thickness on bedrock. Grades and interfingers downslope Qac with debris-fan deposits (Qdf). Includes boulder block fields of frost-wedged and fractured granitic rocks. Soils primarily Byron and Pyle series (Rasmussen, 1981). Thickness 2-20 feet.

Qaf Qcg Outwash of Pinedale age, undivided (late Pleistocene)—Coarse sand with a Qos Qas2 Qop silty fine sand matrix. Forms partially drowned terrace formerly above the Qac modern flood plain. Outwash grades northward to Pinedale moraines in the Qas 2 McCall quadrangle. Soils primarily Donnel and Roseberry series (Rasmussen, 1981). Thickness more than 10 feet.

Qdf Qos Outwash side-stream deposits , undivided (late Pleistocene)—Mostly brown Qts Qal silty to clayey sand. Becomes gravelly upslope where unit grades and m interfingers with debris-fan deposits (Qdf). Deposited by meltwater streams from West Mountain glaciers. Includes minor, mostly inset Holocene stream Qas 2 channels and alluvium. Unit mostly submerged in Cascade Reservoir. Soils primarily Nisula series (Rasmussen, 1981). Thickness 5-50 feet. Qcg Qal Qops Outwash side-stream deposits of Pinedale age, undivided (late Pleistocene)— Mostly brown to gray silty sand. Becomes gravelly upslope closer to glacial Qac Qalo source area. Deposited by meltwater streams from West Mountain glaciers. Qos Includes minor, mostly inset Holocene stream channels and alluvium. Unit Qas 1 mostly submerged in Cascade Reservoir. Soils primarily Gestrin series, but Qts Qal characteristics trend toward Nisula because of component of basalt detritus (Rasmussen, 1981). Thickness 5-50 feet. Qac m Qas2 Qobs Outwash side-stream deposits of Bull Lake age (late Pleistocene)—Silty, clayey Qb sand grading downward into stratified medium to coarse sand. Forms dissected Qdf terrace characterized by low undulating topography. Edge of terrace is diffuse Qac and irregular owing to local erosion graded to younger stream systems. Soil primarily Archabal series (Rasmussen, 1981). Thickness10-60 feet.

Qta m COLLUVIAL DEPOSITS AND BEDROCK

Qcg Colluvium derived from granitic rocks (Holocene and Pleistocene)—Mostly Qal sandy grus derived from the Idaho batholith. Common outcrops of weathered granite and gneiss. Locally includes old erosion surfaces, lag deposits, and Qac Qts Qos Qcg tors. Soils primarily Jugson and Shellrock series (Rasmussen, 1981). Thickness Qta 2-10 feet).

Qas2 sg Qac m sg Ice-scoured granitic bedrock, grus residuum, and Holocene colluvium—Soils Qalo Qal Qal not mapped in area of unit (Rasmussen, 1981). Qalo

Qas2 SYMBOLS Base map scanned from USGS film-positive base, 1985. Field work conducted 2004. MN SCALE 1:24,000 Topography by photogrammetric methods from aerial photographs taken 1 0.5 0 1 This geologic map was funded in part by the USGS National Cooperative Contact: Line showing the boundary between one map unit 1980. Field checked 1981. Map edited 1985. MILE Geologic Mapping Program. and another; dashed where approximately known. The GN FEET Projection Transverse Mercator. 1927 North American Datum. 0o 39 17o 30 1000 0 1000 2000 3000 4000 5000 6000 7000 Digital cartography by Jane S. Free and Loudon R. Stanford at the Idaho location accuracy of a contact is more than 80 feet on 10,000-foot grid ticks based on Idaho coordinate system, west zone. Geological Survey’s Digital Mapping Lab. the ground. KILOMETER IDAHO Note on printing: The map is reproduced at a high resolution of 600 dots per 1000-meter Universal Transverse Mercator grid ticks, zone 11. 1 0.5 0 1 inch. The inks are resistant to run and fading but will deteriorate with long- Contour interval 20 feet QUADRANGLE term exposure to light. UTM Grid and 1985 Magnetic North LOCATION Declination at Center of Map PDF map (Acrobat Reader) may be viewed at www.idahogeology.org. Map version 11-2-2006. Gravel pit that exposes a map unit.

CORRELATION OF MAP UNITS REFERENCES Artificial Deposits Alluvial Deposits Glacial Deposits Colluvium Colman, S.M., and Pierce, K.L., 1981, Weathering rinds on basaltic and andesitic Till Outwash stones as a Quaternary age indicator, Western United States: U.S. Geological mQb HISTORICAL Survey Professional Paper 1210, 56 p. Coleman, S.M., and Pierce, K.L., 1983, The glacial sequence near McCall, Idaho: HOLOCENE Qaf Qal Qas1 Weathering rinds, soil development, morphology and other relative-age ? ? Qcg criteria: U.S. Geological Survey, Open File Report, 83-724, 29 p. Qalo Qas Qac sg ? Qta Mears Jr., Brainerd, 1974, The evolution of the Rocky Mountain Glacial Model, ? Qas2 Qop Qops QUATERNARY in Donald R. Coates ed. Glacial Geomorphology, Publications in ? ? ? Geomorphology, State University of New York, Binghamton, p.11-40. PLEISTOCENE Qos Qdf Qts sg Othberg, Kurt L., 1987, Landforms and surface deposits of Long Valley, Valley County, Idaho: Idaho Geologic Survey Map 5. Qas3 Qobs Rasmussen, L.M., 1981, Soil survey of Valley area, Idaho, parts of Adams and Valley counties: U.S. Department of Agriculture, Soil Conservation Service, sg 146 p. Schmidt, D.L., and Mackin, J.H., 1970, Quaternary geology of Long and Bear TERTIARY Valleys, west-central Idaho: U.S. Geological Survey Bulletin 1311-A, 22 p. ?

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