IDAHO GEOLOGICAL SURVEYMOSCOW-BOISE-POCATELLO

GEOLOGIC MAP 27BUSH, PIERCE, AND POTTER

Published and sold by the Idaho Geological SurveyUniversity of Idaho, Moscow, Idaho 83844-3014

Reviewed by Roy M. Breckenridge and Kurt L. Othberg, Idaho Geological Survey.

Field work conducted 1997-1998.Digital cartography by Vance T. MacKubbin and Jane S. Freed at the

Idaho Geological Survey’s Digital Mapping and GIS Lab.

Base map from USGS digital raster graphic 1972.Topography by photogrammetric methods from aerial photographs taken1957. Field checked 1960.Polyconic projection. 1927 North American Datum.10,000-food grid ticks based on Idaho coordinate system, west zone.1000-meter Universal Transverse Mercator grid ticks, zone 11.

BEDROCK GEOLOGIC MAP OF THE MOSCOW EAST QUADRANGLE, LATAH COUNTY, IDAHO

John H. Bush, Jack L. Pierce, and Gerald N. Potter

2000

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SYMBOLS

Contact: approximately located

Fault: approximately located; ball and bar on downthrown side

Attitude of major foliation trends

Attitude of bedding in quartzites

REFERENCES

Anderson, M.A., 1991, The geology and structural analysis of the Tomer Butte,Middle Potlatch Creek and Little Potlatch Creek area, Latah County, Idaho:University of Idaho M.S. thesis, 69 p.

Bingham, J.W., and M.J. Grolier, 1966, The Yakima Basalt and EllensburgFormation of south-central Washington: U.S. Geological Survey Bulletin1224-G, 15 p.

Bond, J.G., 1978, Geologic map of Idaho: Idaho Bureau of Mines and Geology,scale 1:500,000.

Brown, J.C., 1976, Well construction and stratigraphic information, Pullman testand observation well, Pullman, Washington: Washington State University,College of Engineering Research Report 76/15-6, 35 p.

Bush, J.H., A.P. Provant, and S.W. Gill, 1998, Bedrock Geologic Map of theMoscow West quadrangle, Latah County, Idaho and Whitman County,Washington: Idaho Geological Survey Geologic Map 23, scale 1:24,000.

Cavin, R.E., 1964, Significance of the interbasalt sediments in the Moscow basin,Idaho: Washington State University M.S. thesis, 97 p.

Hammerand, V.F., 1936, Geology and petrology of a part of the Paradise Ridgein northwestern Idaho: University of Idaho M.S. thesis, 25 p.

Hooper, P.R., and G.D. Webster, 1982, Geology of the Pullman, Moscow West,Colton, and Uniontown 7.5-minute quadrangles, Washington and Idaho:Washington Division of Geology and Earth Resources, Geologic Map GM-26, scale 1:62,000.

Hooper, P.R., G.D. Webster, and V.E. Camp, 1985, Geologic map of the Clarkston15-minute quadrangle, Washington and Idaho: Washington Division ofGeology and Earth Resources, Geologic Map GM-31, 11 p., 1 pl., scale1:48,000.

Hosterman, J.W., V.E. Scheid, V.T. Allen, and I.G. John, 1960, Investigations ofsome clay deposits in Washington and Idaho: U.S. Geological Survey Bulletin1091, 147 p.

Hubbard, C.R., 1956, Clay deposits of north Idaho: Idaho Bureau of Mines andGeology Pamphlet 109, 36 p.

Lin, Chang-Lu, 1967, Factors affecting ground water recharge in the Moscowbasin, Latah County, Idaho: Washington State University M.S. thesis, 86 p.

Kopp, W.P., 1994, Hydrogeology of the upper aquifer of the Pullman-Moscowbasin at the University of Idaho aquaculture site: University of Idaho M.S.thesis, 142 p.

Pierce, J.L., 1998, Geology and hydrogeology of the Moscow East and RobinsonLake quadrangles, Latah County, Idaho: University of Idaho M.S. thesis, 84p.

Reidel, S.P., T.L. Tolan, P.R. Hooper, M.H. Beeson, K.R. Fecht, R.D. Bently, andJ.L. Anderson, 1989, The Grande Ronde Basalt, Columbia River Basalt Group:Stratigraphic descriptions and correlations in Washington, Oregon, andIdaho, in S.P. Reidel and P.R. Hooper, eds., Volcanism and Tectonism in theColumbia River Flood-Basalt Province: Geological Society of America SpecialPaper 239, p. 21-54.

Rember, W.C., and E.H. Bennett, 1979, Geologic map of the Pullman quadrangle,Idaho: Idaho Bureau of Mines and Geology, scale 1:250,000.

Siems, B.A., J.H. Bush Jr., and J.W. Crosby, III, 1974, TiO2 and geophysicallogging criteria for Yakima Basalt correlation, Columbia Plateau: GeologicalSociety of America Bulletin, v. 85, p. 1061-1068.

Swanson, D.A., J. L. Anderson, R.D. Bentley, G.R. Byerly, V.E. Camp, J.N. Gardner,and T.L. Wright, 1979a, Reconnaissance geologic map of the ColumbiaRiver Basalt Group in eastern Washington and northern Idaho: U.S. GeologicalSurvey Open-File Report 79-1363, scale 1:250,000.

Swanson, D.A., T.L. Wright, V.E. Camp, J.N. Gardner, R.T., Helz, S.A. Price, andM.E. Ross, 1977, Reconnaissance geologic map of the Columbia River BasaltGroup, Pullman and Walla Walla quadrangles, southeast Washington andadjacent Idaho: U.S. Geological Survey Open-File Report 77-100, scale1:250,000.

Swanson, D.A., T.L. Wright, V.E. Camp, J.N. Gardner, R.T. Helz, S.A. Price, andM.E. Ross, 1980, Reconnaissance geologic map of the Columbia River BasaltGroup, Pullman and Walla Walla quadrangles, southeast Washington andadjacent Idaho: U.S. Geological Survey Miscellaneous Geologic InvestigationsMap I-1139, scale 1:250,000.

Swanson, D.A., T.L. Wright, P.R. Hooper, and R.D. Bentley, 1979b, Revisionsin stratigraphic nomenclature of the Columbia River Basalt Group: U.S.Geological Survey Bulletin 1457-G, 59 p.

Tullis, E.L., 1940, Geology and petrography of Latah County, Idaho: Universityof Chicago Ph.D. thesis, 218 p.

Tullis, E.L., 1944, Contribution to the geology of Latah County, Idaho: GeologicalSociety of America Bulletin, v. 55, p. 131-164.

Webster, G.D., and L. Nunez, 1980, Geology of the steptoes and Palouse Hillsof eastern Washington: A roadlog of the area south of Spokane, Washington:Tobacco Root Geological Society Guidebook, 93 p.

Wright, T.L., M.J. Grolier, and D.A. Swanson, 1973, Chemical variation relatedto the stratigraphy of the Columbia River basalt: Geological Society ofAmerica Bulletin, v. 84, no. 2, p. 371-385.

PREBASALT ROCKS

Undifferentiated intrusive rocks (Cretaceous)—Undifferentiated intrusive andmetamorphosed intrusive rocks. Most exposures consist of medium-grained(2 to 3 mm) granodiorite with gneissic foliation. Pegmatitic zones are locallycommon. Similar rocks on nearby quadrangles have been dated as LateCretaceous (Webster and Nunez, 1980; Hooper and Webster, 1982).

Mixed rocks (Precambrian-Cretaceous)—Consists of mixed units of granodiorite,gneiss, schist, and quartzite. Thinly banded black and white schist and gneissdominate the unit. Quartzites are recrystallized, with bedding and foliationdestroyed in most places. Granodiorite, which in places is pegmatitic, followsand cross-cuts the foliation of the other units.

Quartzite, schist, and gneiss (Precambrian)—Consists of interlayered units ofquartzite, schist, and gneiss. The quartzite consists primarily of recrystallizedquartz with muscovite, biotite, and zircon accessories. Mapping on thisquadrangle and adjoining quadrangles to the north and east suggests thesequartzites are resistant remnants from a unit of quartzite, gneiss, and schistrather than a unit dominated by quartzite. On the Moscow East and adjoiningTroy quadrangles, quartzites form the top of Tomer Butte. However, rareexposures of schist and gneiss are found in gullies and roadcuts on the flanksof the butte.

Quartzite (Precambrian)—Consists of recrystallized quartz with muscovite,biotite, and zircon accessories. Bedding is indistinct in most outcrops. Theunit may be part of the quartzite, schist, and gneiss unit discussed above.However, on Paradise Ridge the transition from quartzite to gneiss andgranitoid rock of the Idaho batholith occurs over a short distance (Hammerand,1936), and it can be mapped as a separate unit.

1 KILOMETER

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COLUMBIA RIVER BASALT GROUP

PREBASALT ROCKS

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Saddle Mountains Formation

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LATAH FORMATION

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TERTIARY

CORRELATION OF MAP UNITS

INTRODUCTION

The geologic map of the Moscow East quadrangle represents a compilationof previous research, water well data (Pierce, 1998), and additional fieldwork. The loess distribution of the Palouse Formation was not illustrated inkeeping with the emphasis on bedrock geology. Outcrops are rare, and thecontact lines are interpretive. Regional maps by Rember and Bennett (1979)and Swanson and others (1977, 1979a, 1980) as well as maps by Tullis(1940, 1944) were used in the compilation. The basalt chemistry was analyzedby the GeoAnalytical Laboratory at Washington State University.

DESCRIPTION OF MAP UNITS

Prebasalt rocks here and on the surrounding quadrangles have been mappedas several different units, including Precambrian pre-Belt Supergroup, BeltSupergroup, metamorphosed Belt Supergroup, Cambrian quartzite, andCretaceous metamorphosed and unmetamorphosed Idaho batholith intrusiverocks (Tullis, 1940, 1944; Bond, 1978; Swanson and others, 1980; Remberand Bennett, 1979; Hooper and Webster, 1982; and Anderson, 1991). Forthis map, the prebasalt rocks were divided into a Precambrian unit ofquartzite, gneiss, and schist, a Precambrian quartzite unit, a mixed unit ofPrecambrian and Cretaceous rocks, and a Cretaceous unit of undifferentiatedIdaho batholith rocks.

The stratigraphic nomenclature for the Columbia River Basalt Group is basedon that presented by Swanson and others (1979b). The group is divided intofour formations: from base upward, these are the Imnaha, Grande Ronde,Wanapum, and Saddle Mountains. No basalt of the Imnaha and GrandeRonde is exposed in the Moscow East quadrangle. However, the GrandeRonde is found in numerous deep wells in the Moscow area.

Overlying the basalt flows is a deposit of unconsolidated sediments of theLatah Formation. Earlier researchers referred to these sediments as theCanfield-Rogers deposit (Hubbard, 1956; Hosterman and others, 1960).There are similar deposits throughout Latah County. Informally, this unit isnamed herein as the sediments of Bovill for exposures in clay pits near Bovillin eastern Latah County. The term is to be used for Miocene sediments thatare laterally equivalent with and generally overlie the uppermost laterallyextensive basalt flow. In places, the sediments lie directly on prebasalt rocks.Terminology for Latah sediments between and beneath basalt units in theMoscow area follows that of Bush and others (1998).

SURFICIAL DEPOSITS

Alluvium and colluvium (Holocene)—Stream, slope-wash, and debris-flowdeposits. Compositions varied: commonly reworked loess or mixtures ofloess, basalt, and granitoid fragments. Most occurrences are stream depositsthat grade laterally into loess of the Palouse Formation and contain slope-wash deposits derived from the loess-covered hills. The upper regions ofdrainages from Tomer Butte and Paradise Ridge consist of poorly sorted andangular to subangular deposits of quartz and quartzite granules and pebbles.

LATAH FORMATION

Sediments of Bovill (Miocene)—Clay, silt, sand, and gravel deposit that islaterally equivalent and generally overlies the Priest Rapids Member of theColumbia River Basalt Group. In places, it overlies prebasalt rocks. The claysare white, yellow, red, and brown, kaolinite-rich, and in places more than200 feet thick. The sands and gravels are typically poorly sorted in a claymatrix. It is not uncommon to find poorly rounded quartz and basalt granulesand pebbles in a matrix of silt and clay. Exposures are rare, but in placesthey are visible beneath thin loess deposits. The distribution of these sedimentswas determined from well data and foundation excavations.

Depositional information for the sediments of Bovill was obtained fromregional studies. Upward-fining sequences of gravel or sand to clay arecommon close to source areas, and sequences of minor silt overlain by thickclay units are common away from source areas. The sediments of Bovillhave several origins ranging from in situ weathered granite to shallowlacustrine deposits. However, most of these sediments are believed to haveformed as fluvial deposits. Deposition was primarily caused by Priest Rapidsflows creating a raised base level, which in turn caused the deposition ofkaolinitic clay, quartz sand, and minor gravel from streams eroding nearbyexposures of weathered prebasalt rock.

Vantage Member (Miocene)—Consists of sediments between the lowermostPriest Rapids and uppermost Grande Ronde in the Moscow-Pullman area(Siems and others, 1974; Brown, 1976; Knopp, 1994). The unit exceeds 300feet in thickness beneath Moscow but thins westward to less than 20 feetin thickness at Pullman (Lin, 1967). The Vantage is not exposed in Moscow.All data are from water well logs. The sediments consist of interlayered sand,silt, and clay. Wood fragments are commonly found. The sand units arepoorly sorted with a high clay content, and the coarse grains of quartz andfeldspar are angular with only slightly rounded edges (Cavin, 1964).

Sediments of Moscow (Miocene)—Interbeds of sand, silt, and clay betweenGrande Ronde flows and between the lowermost flow and prebasalt rocks.Several discontinuous interbeds are in the subsurface beneath Moscow.However, two major units over 100 feet thick can be correlated betweenwater wells (Cavin, 1964; Lin, 1967). Eastward, the sand content increasesas does the grain size. Westward, these interbeds pinch out or thin to lessthan a few feet in thickness at Pullman (Brown, 1976).

COLUMBIA RIVER BASALT GROUP

Saddle Mountains Formation

Weissenfels Ridge Member (Miocene)—Medium- to coarse-grained basaltwith microphenocrysts of plagioclase and olivine in an intergranulargroundmass with minor glass (Hooper and others, 1985). In the Pullmanarea, outcrops of this member belong to the basalt of Lewiston Orchards(Hooper and Webster, 1982). Exposures on the Moscow East quadrangle aresimilar in hand specimen, chemistry, and magnetic polarity to the outcropsmapped by Hooper and Webster (1982). The flows of Lewiston Orchardsare interpreted as valley-filling basalt overlying the Priest Rapids Memberwithout great lateral extent.

Wanapum Formation

Priest Rapids Member (Miocene)—Medium- to coarse-grained basalt withmicrophenocrysts of plagioclase and olivine in a groundmass of intergranularpyroxene, ilmenite blades, and minor devitrified glass. Well data andexposures suggest the unit consists of one or two flows with a compositethickness of 160-200 feet. Several workers have previously identified anddescribed these flows (Bingham and Groilier, 1966; Wright and others, 1973;Swanson and others, 1977, 1979b). The flows have reversed magneticpolarity (Wright and others, 1973; Swanson and others, 1979b).

The member is exposed in numerous roadcuts throughout the quadrangle,but no exposures of contacts between individual flow units and flows werenoted. Hooper and Webster (1982) report three chemical types of thismember in the Pullman-Moscow area to the west and northwest.

Grande Ronde Formation (Miocene)—Consists of fine-grained to very fine-grained aphyric flows of Grande Ronde chemical type (Wright and others,1973; Swanson and others, 1977, 1979a; Reidel and others, 1989). Noexposures occur in the mapped area, but the formation is present belowWanapum flows in wells over 300 feet deep.

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