U.S. Department of the Interior Prepared in cooperation with the OPEN-FILE REPORT 2012–1170 U.S. Geological Survey Montana Bureau of Mines and Geology

112°00' 110°00'

49°00' 111°30' 111° 110°30' 49°00'

%

% LATE WISCONSIN

% % lse %

%% % Wild Horse Lake LIST OF MAP UNITS DESCRIPTION OF MAP UNITS SOURCES OF INFORMATION % B %

% % lu

% % %

k e % % a % %

e IT tlx al % lca [Map unit thickness is typical range; in some areas the map units may be thicker or LOAMY TILL—Sediment deposited chiefly by ice of a Laurentide continental ice Alden, W.C., 1924, Physiographic development of the northern Great Plains: Geological

re r lca % C % %

C % IT

re tlx R thinner than the given range] sheet. Informal Fort Assiniboine till of Fullerton and Colton (1986). The till in the Society of America Bulletin, v. 35, p. 385–423.

% jea ard e HOLOCENE AND LATE WISCONSIN

% ch k IT

% i % %

r %

% % %

%% P tlx % northwestern part of the quadrangle was deposited by the Shelby glacial lobe; the Alden, W.C., 1932, Physiography and glacial geology of eastern Montana and adjacent areas:

%

lss % % R % al

%

% cly % FLOOD-PLAIN AND CHANNEL ALLUVIUM % % % % till in the northeastern part of the quadrangle was deposited by the Havre glacial % lu % % % U.S. Geological Survey Professional Paper 174, 133 p. %

% 150 % lss Wild Horse Lake HOLOCENE AND LATE WISCONSIN

% 0 %

% lobe; the till in the southeastern part of the quadrangle was deposited by the Loma Calhoun, F.H.H., 1906, The Montana lobe of the Keewatin ice sheet: U.S. Geological Survey %

crr % al FLOOD-PLAIN AND CHANNEL ALLUVIUM—Yellowish-brown, olive-brown, %

% % % %% % % % afj % % gg %

% ALLUVIAL-FAN DEPOSITS

%

%% % glacial sublobe (fig. 1). Regional ice flow patterns are recorded by ice-molded or Professional Paper 50, 62 p. %% % %

%

%% al % grayish-brown, brown, olive, yellowish-gray, brownish-gray, olive-gray, gray,

% tlx % % %

% % %

% % % West ice-scoured landforms (shown by a symbol) and by the orientations of till ridges Christiansen, E.A., 1979, The Wisconsinan deglaciation of southern Saskatchewan and adjacent % % wla

k La LOAMY AND CLAYEY SHEETWASH ALLUVIUM black, or mottled clay, silt, sand, and gravel. Calcareous or noncalcareous; partly

% %% e ird Cree tlx

%

cly Butte e k % and meltwater channels (also shown by symbols). Typical till is pale-yellow, % areas: Canadian Journal of Earth Sciences, v. 16, p. 913–938.

tlx r lu % or completely oxidized. Clasts angular to well rounded. Clast composition

%% lse

% al C %

%

% tlx % grayish-yellow, yellowish-brown, olive-brown, grayish-brown, brown, %

tlx(s) er ek % lca LAKE CLAY AND SILT reflects composition of other surficial materials and bedrock in the drainage basin. Clayton, Lee, and Moran, S.R., 1982, Chronology of late Wisconsinan glaciation in middle % e % %

cad e Cr %

lss D Sage brownish-olive, olive, yellowish-gray, brownish-gray, olive-gray, bluish-gray, gray, North America: Quaternary Science Reviews, v. 1, p. 55–82.

% %

%

S R % Fossiliferous (gastropod, pelecypod, and vertebrate remains; wood fragments and

% % %

W % tlx(e) %

jea % lss or mottled, calcareous clay loam and loam; in some areas it is clay, silty clay, silty % % Colton, R.B., Lemke, R.W., and Lindvall, R.M., 1961, Glacial map of Montana east of the

%

% LAKE SILT AND SAND %

% EET % plant detritus) in some places. Included in other map units in many areas. % %

%

ke %

tlx M clay loam, silt loam, sandy clay, or sandy loam. Very gravelly in some places; Rocky Mountains: U.S. Geological Survey Miscellaneous Geologic Investigations % jea il % Includes some sheetwash alluvium, alluvial-fan deposits, alluvium beneath low % G k % R R lu where till directly overlies shale bedrock, the matrix commonly is >90 percent

lca % i LAKE CLAY, SILT, SAND, AND GRAVEL Map I-327, scale 1:500,000.

tlx(e) A pgd tlx(e) v terraces, outwash and ice-contact sand and gravel, lake deposits, and bedrock

S lca e lu r % % lss %% % S tlx % shale fragments. In some places, till is interbedded with, intercalated with, or De Young, William, Youngs, F.O., and Glassey, T.W., 1932, Soil survey of the Milk River area,

Sunburst lu HIL lu tlx(e) outcrops. Alluvium in some areas is dominantly redeposited outwash, ice-contact

gg tlx( lse LAKE AND EOLIAN SAND AND SILT contains lenses, pods, and stringers of clay, silt, sand, or gravel. Generally Montana: U.S. Department of Agriculture, Bureau of Chemistry and Soils, Series 1928, % % %

% gg deposits, and lake deposits. East and northeast of Big Sandy, alluvium overlies a

%

tlx % e)

% % %

% LS

% % nonstratified; nonsorted or very poorly sorted. Local weak horizontal layering no. 22, 35 p. % %

% % %

% thick fill of older fluvial, glaciofluvial, and glaciolacustrine deposits and till (see

%

% 1 cad

% % ls

cly 000 ke s COLLUVIUM, SHEETWASH ALLUVIUM, LAKE DEPOSITS, AND where the ice margin fluctuated in a lake. Commonly massive; cohesive to friable. Dyke, A.S., 2004, An outline of North American deglaciation with emphasis on central and

%

crr crr % description of till deposits associated with “Buried bedrock valleys of the ancestral %

tlx(e) %

%

R % % %

%

% In some areas, gritty or mealy; crude fissility. Generally loosely compact or northern Canada, in Ehlers, Juergen and Gibbard, P.L., eds., Quaternary %

cad % GLACIOFLUVIAL-FILL DEPOSITS

%

IT pgd % Marias and Missouri Rivers” in the Explanation of map symbols). Thickness 1–6

% % % %

% % crr %

tlx %

%% Gold k caa compact, but not hard. Sandy till is loose to firm; silty till is firm. Clayey till is glaciations—Extent and chronology, Part 2, North America: Amsterdam, Elsevier, p.

%

% ee COLLUVIUM, SHEETWASH ALLUVIUM, AND LANDSLIDE DEPOSITS m, locally >15 m

%

% tlx(e) pgd r %

C East %

% % %

Butte ry al % soft, slightly sticky to sticky, and slightly plastic to plastic when moist; hard when 373–430. %%

%

% r Flood-plain alluvium—Chiefly poorly-sorted to well-sorted clay, silty clay, silty clay %

e % % % %

% 1 b Butte tlx

500 w lss R dry. Dry till in some places breaks into small angular flakes and plates that have Fox, P.P., 1946, Buried Pleistocene gorge of the Marias River, Montana [abs.]: Geological % %

% % %

jea %

% cad a %

r jea L tlx HOLOCENE, LATE PLEISTOCENE, AND MIDDLE PLEISTOCENE loam, clayey silt, and silt with scattered granules and pebbles; locally, loam, sandy % % caa t

% % lca

%

S pgd it % sharp edges; blocky structure in some other places. Parting typically is irregular or Society of America Bulletin, v. 57, no. 12, p. 1194.

% tl tlx(e) clay loam, sandy loam, or fine sand. Moderately to well stratified. Commonly has % %

% % e

%

%

% % % % %

lu % cly Sa cly LOAMY COLLUVIUM prismatic. Clay minerals are dominantly montmorillonite. Widely spaced, Fullerton, D.S., Christiansen, E.A., Schreiner, B.T., Colton, R.B., and Clayton, Lee, 2007, %

caa % afj ge gg either obscure bedding or pronounced horizontal bedding; weakly laminated in % % C

%

R % lca

ree tlx weakly-developed joints are common; in some places, joint surfaces are coated by Quaternary geologic map of the Regina 4° × 6° quadrangle, United States and Canada: %

pgd k Frank Jurenka’s % some places. Clay, silt, sand, or gravel lenses or small channel fills of sand and

% %

% % %

pgd Reservoir % crr %

tlx % FROST-RUBBLE AND TALUS-RUBBLE DEPOSITS powdery calcium carbonate or gypsum, or both. Joint or parting surfaces are U.S. Geological Survey Miscellaneous Investigations Series Map I–1420 (NM–13), 37 % % % % %

% % gravel are common. Dense and compact in most places. Clayey alluvium is

% lu %

%

lca % locally weakly stained by iron or manganese oxides. Selenite (gypsum) crystals p., map scale 1:1,000,000.

% % % % moderately plastic, soft, and sticky where moist and hard where dry. Textures may

%%

%

% %

% % % % al % % % % 1–3 mm long are present on joint surfaces in some places. Fragments of lignite Fullerton, D.S., and Colton, R.B., 1986, Stratigraphy and correlation of the glacial deposits on % % %

caa % HOLOCENE AND PLEISTOCENE vary abruptly, laterally and vertically. Local thin buried soils (humic horizons).

% % lu

R % % (bedrock) are ubiquitous in till. Nearly pebble free to very pebbly; cobbles and the Montana Plains, in Richmond, G.M., and Fullerton, D.S., eds., Quaternary

% % % R jea Concentrations of detrital lignite (bedrock) fragments as large as 1 cm are common %

% % gg al al SLUMP-BLOCK LANDSLIDE DEPOSITS AND ROCKSLIDE DEPOSITS

% % %

% boulders are rare to abundant. Largest erratic boulders are >2 m in diameter. glaciations in the United States of America: Quaternary Science Reviews, v. 5, p. %

lu % kg % % in crossbedded sand. Where flood-plain alluvium directly overlies lake clay, silt,

% %% lu %

%% % % lu

% % lu and sand or sheetwash alluvium, in some places it is difficult to distinguish the Clasts of older till and clasts of lignite (bedrock) as large as 2 m in diameter locally 69–82.

%

lu % L

%

% cad i lss

%

% lca ttl LATE WISCONSIN are included in the till. Glaciotectonic blocks or rafts of shale or sandstone tens of Fullerton, D.S., Colton, R.B., and Bush, C.A., 2004, Limits of mountain and continental %

% e % % %

% S

%% ag lse deposits % % %

gg % k e % % % % %

% C

tlx % % lu ee reek meters in length locally are included in the till. Pebbles in typical till are chiefly glaciations east of the Continental Divide in northern Montana and north-western North % %

%

% r lss LOAMY TILL Channel alluvium—Chiefly loose, stratified, poorly-sorted to well-sorted, pebbly, fine

% % % C tlx % % % % % %

%

Kevin %% % ep lu tlx subangular to rounded erratic limestone and dolomite and erratic igneous and Dakota, U.S.A., in Ehlers, Juergen, and Gibbard, P.L., eds., Quaternary %

% e tlx to medium sand and (or) coarse sand and gravel; locally very poorly sorted sandy

% Sh lss Ground-moraine deposits

% % %

% tlx(e) % lu metamorphic rocks from the Canadian Shield; where till is derived primarily from glaciations—Extent and chronology; Part 2, North America: Amsterdam, Elsevier, p. % %

%

% lu shale gravel. Cobbles and boulders are common to abundant in some areas.

% %

%

% k tlx(e) local bedrock, pebbles are chiefly angular to subrounded shale, siltstone, and soft 131–150. %

% e R % % % % W C End-moraine deposits

%

% e gg o % % r % % Generally crossbedded or has crude horizontal bedding or lenticular bedding; local i r tlx(s) l C r

l a sandstone; where derived from Tertiary and Quaternary gravel, pebbles are chiefly Fullerton, D.S., Colton, B.B., and Bush, C.A., 2011, Quaternary geologic map of the Havre 1°

%

% o il l tlx %

% w lu C lse festoon bedding. Locally fossiliferous (chiefly vertebrate remains) %

tlx(e) % a re tlx(s)

%

% r quartzite, argillite, chert, and chert conglomerate from the mountains to the west or x 2° quadrangle, Montana: U.S. Geological Survey Open-file Report 2011–1028, map e Stagnation-moraine deposits

%

% IT C T k % lu % Re

r Fresno s

e er volcanic rocks from the south. Cobbles and boulders are chiefly subangular to scale 1:250,000.

lu e v %

% o afj k %

% ir ke ALLUVIAL-FAN DEPOSITS—Yellowish-brown, grayish-brown, yellowish-gray,

caa E KAME-MORAINE DEPOSITS well-rounded, erratic granite, pegmatite, gneiss, schist, diorite, and other igneous Fullerton, D.S., Colton, R.B., Bush, C.A., and Straub, A.W., 2004, Map showing spatial and

%

% a

%

% G

lss g brownish-gray, gray, or mottled clay, silt, sand, and gravel. Calcareous. Poorly to

%

% gg % % Howard Sailors Reservoir

lu o

lu l and metamorphic rocks from the Canadian Shield; less abundant erratic limestone temporal relations of mountain and continental glaciations on the Northern Plains, % % lu

% % e

caa v lss % lss

%

e well stratified; poorly to well sorted. Poorly-sorted gravel and pebbly sand near

%

% kg %

% C tlx(e) % % %

% ICE-CONTACT SAND AND GRAVEL

r and dolomite from Saskatchewan and Manitoba, and quartzite from the Rocky primarily in Montana and northwestern North Dakota: U.S. Geological Survey

al r

n

%

lss %

e

%

% m fan apex, grading to pebbly silt and clay near toe. Clasts are subangular to well e

% % lu

%

% k Mountains. Till everywhere is generally unstable; it moves by creep on hillslopes; Scientific Investigations Map SIM–2843, 36 p., map scale 1:1,000,000. e %

% gg

n rounded, reworked cobbles, pebbles, and granules derived from pediment,

% %

%

% lu kg OUTWASH SAND AND GRAVEL

t %

lu % slumps in exposures. Till is thin and discontinuous in many areas; locally the map Giesecker, L.F., Morris, E.R., Strahorn, A.T., and Manifold, C.B., 1933, Soil survey %

% C

% %

%

% alluvial-fan, and fluvial-terrace deposits (pgd), till, and local bedrock. Includes %

r tlx % % %

%

tlx % lu e lu unit includes exhumed till of Illinoian and (or) pre-Illinoian age that is exposed at (reconnaissance) of the Northern Plains of Montana: U.S. Department of Agriculture, %

e %

%

% lda

%

% k % % LAKE DENSITY-CURRENT UNDERFLOW-FAN DEPOSITS some sheetwash alluvium and flood-plain and channel alluvium. Mapped as an

% %

%

lu % lu Chain of

lu H the surface. Includes some glaciotectonic deposits (symbol IT), flowtill, mud-flow Bureau of Chemistry and Soils, ser. 1929, no. 21, 74 p.

%

% o k Lakes lu alluvial-fan complex east of the East Butte of the Sweet Grass Hills. Small % % % % % % % % lss

tlx rs g

e lss and debris-flow deposits, and landslide deposits. Includes areas of till that were Hill, C.L., 2002, Late Quaternary stratigraphy and radiocarbon chronology from the lower %

al C % lss ldb

% % DELTA SAND AND GRAVEL

%

% D r alluvial-fan deposits are included in other map units. Thickness 0.5–10 m; %

caa % % e modified by waves and currents in glacial lakes, with a surface litter of cobbles and Marias River Valley, northern Montana: American Quaternary Association (AMQUA),

r e

% y %

% % % k %

%

% maximum thickness >10 m % %

%

F %

% % % % boulders or a discontinuous cover of lake clay, silt, and sand. Includes some lake 17th biennial meeting, Anchorage, Alaska, Program and Abstracts, p. 68.

tlx o

r lu

%

k lu % PLEISTOCENE AND PLIOCENE 1 delta deposits, outwash and ice-contact sand and gravel, flood-plain and channel Horberg, Leland, and Robie, R.A., 1955, Postglacial volcanic ash in the Rocky Mountain

%

W % lca lss lss lss wla LOAMY AND CLAYEY SHEETWASH ALLUVIUM —Pale-yellow,

%

% il pgd

R l lu kg alluvium, and bedrock outcrops. Locally overlain by colluvium, sheetwash piedmont, Montana and Alberta: Geological Society of America Bulletin, v. 66, p. %

caa % o lu PEDIMENT, ALLUVIAL-FAN AND FLUVIAL-TERRACE DEPOSITS % % yellowish-brown, olive-brown, brown, olive, yellowish-gray, olive-gray,

Aloe Lake w alluvium, lake clay, silt, and sand, or eolian sand and silt.

C tlx(e) kg 949–955.

%

% re brownish-gray, gray, or mottled alluvium transported and deposited by unconfined

% Kemp, J.F., and Billingsley, Paul, 1921, Sweet Grass Hills, Montana: Geological Society of e % % % PRE-QUATERNARY

k kg overland flow and rill wash. Clay, silty clay, silty clay loam, and clay loam.

%% tlx Ground-moraine deposits—Integrated drainage; flat, rolling, or undulating surface America Bulletin, v. 32, p. 437–478. % % kg R BEDROCK Nonstratified to moderately well stratified; poorly or moderately well sorted. tlx tlx C lss topography. In some places, includes some collapsed supraglacial sediment Lemke, R.W., Laird, W.M., Tipton, M.J., and Lindvall, R.M., 1965, Quaternary geology of the lu lss o t

lu t ke Massive, thinly laminated, or with weak horizontal bedding. Disseminated organic

o

% lu % (stagnation moraine deposits) and small end moraine deposits. Maximum slope northern Great Plains in Wright, H.E., Jr., and Frey, D.G., eds., The Quaternary of the

V n lu Gildford

i w matter is abundant in some places. Fossiliferous (gastropod tests) locally. %

r % %

d % % % EXPLANATION OF MAP SYMBOLS o angles are generally less than 4°. Local relief is generally <3 m. Thickness 0.5–2 United States: Princeton, N.J., Princeton University Press, p. 15–27.

%

o %

e Fragments of lignite (bedrock) are common. Calcareous. Clast free, with scattered

lu d n Joplin % % m; maximum thickness >6 m. Overlies older till in most areas; till thicknesses of Lemke, R.W., Mudge, M.R., Wilcox, R.E., and Powers, H.A., 1975, Geologic setting of the

% % Rudyard

C

% % kg granules and small pebbles, or with stringers, pods, and lenses of granule or pebble

caa kg

L re >10 m generally include thicknesses of older subsurface tills Glacier Peak and Mazama ash-bed markers in west-central Montana: U.S. Geological

tlx(e) e Hingham lss %

a % % % k tlx gravel. Clayey alluvium is soft, sticky, and plastic where moist; tough, hard, and

ke tlx % lu lca % Survey Bulletin 1395-H, p. H1–H31. IT blocky where dry. Clay minerals are dominantly montmorillonite. Granules and

gg Known or suspected glaciotectonic deposits or glaciotectonic tlx(e) End-moraine deposits—Till characterized by (1) broad, long belts of hummocky or Lindvall, R.M., 1956a, Geology of the Kenilworth quadrangle, Montana: U.S. Geological

lss pebbles are chiefly local clastic sedimentary rocks; minor redeposited erratic

%

% terrain—Bedrock and surficial deposits that were thrust, stacked, and undulating ridges or (2) belts of narrow, discontinuous, sharply defined ridges that Survey Miscellaneous Geologic Investigations Map I–129, scale 1:62,500. %

% lu

% % limestone, dolomite, and igneous and metamorphic rocks. Sheetwash alluvium

lu deformed by glacial ice. Chiefly (1) tilted bedrock blocks overlying till and delineate the configurations of vanished ice margins. Large areas mapped between Lindvall, R.M., 1956b, Geology of the Big Sandy quadrangle, Montana: U.S. Geological % % % %

% R % commonly overlaps flood-plain alluvium. Included in other map units in many

cad tlx stratified sediments; (2) stacked or imbricated slices of bedrock, till, and the Sweet Grass Hills are complexes of till ridges. Shallow closed depressions and Survey Miscellaneous Geologic Investigations Map I–130, scale 1:62,500.

% % places in the quadrangle. Mapped only in the Missouri River valley in the stratified sediments that form parallel or concentric ridges; or (3) deformed lag cobbles and boulders are common on the surface in some areas. Local relief in Lindvall, R.M., 196l, Geology of the Boxelder quadrangle, Montana: U.S. Geological Survey

Shelby caa lca southeast corner of the quadrangle and north of the Tiber Reservoir. Thickness 1–4

48°30' Chester masses of bedrock and surficial deposits characterized by overturned folds. some places is 4–>10 m. Till end-moraine deposits are locally replaced laterally by Miscellaneous Geologic Investigations Map I–338, scale 1:62,500. % lca% m tlx Some glaciotectonically transported materials are covered by till that was kame-moraine deposits that are included in the map unit. In some places, Lopez, D.A., 1994, Preliminary geologic map of the Shelby 30' x 60' quadrangle: Montana

lca lss

lca %% % % kg boundaries between end-moraine deposits and stagnation-moraine or Bureau of Mines and Geology Open-file Report MBMG 315, scale 1:100,000. % % deposited by overriding ice. Thickness 5–>30 m % Dunkirk tlx

tlx %% lca LAKE CLAY AND SILT—Pale-yellow, grayish-yellow, bluish-green,

% tlx lu 0 ground-moraine deposits are transitional, and contacts are arbitrary. Thickness Lopez, D.A., 1995, Geology of the Sweet Grass Hills, north-central Montana: Montana Bureau

0 % % % % Lothair % % %

lu 0 yellowish-brown, olive-brown, grayish-brown, brown, olive, yellowish-gray,

% Galata 1 % %% Contact 4–15 m, locally >20 m of Mines and Geology Memoir 68, 35 p. % lu % % lu % % brownish-gray, olive-gray, bluish-gray, gray, olive-black, bluish-black, black, or caa tlx % tlx(e)% Lopez, D.A., 2002a, Geologic map of the Sweet Grass Hills 30’ x 60’ quadrangle, north-central al lca mottled, calcareous clay and silt. Generally stratified; well sorted; massive or tlx(s)

% % Stagnation-moraine deposits—Till characterized by hummocky or knob-and-kettle Montana: Montana Bureau of Mines and Geology Open-file Report MBMG 443, 17 p.,

% lu % weakly bedded. Commonly laminated, locally varved, clay and silty clay in lower lu caa cad Shoreline collapsed topography. Generally lacks distinct, continuous ridges. Nonintegrated map scale 1:100,000. part and massive or horizontally-bedded silty clay and silt in upper part. Upper lu lss lu % %% tlx % or poorly integrated drainage; shallow ephemeral ponds, sloughs, and depressions Lopez, D.A., 2000b, Geologic map of the Conrad 30’ x 60’ quadrangle, north-central Montana: as River lu % part generally is clast free; in some places, iceberg-rafted granules, pebbles, caa ari % are common. Ice-block depressions (kettles) are abundant in some areas. Local Montana Bureau of Mines and Geology Open-file Report MBMG 444, 10 p., map scale M %% Limit of late Wisconsin glaciation on the Sweet Grass Hills lca E lu % % % IT cobbles, and boulders are common in lower part. Clasts generally are absent on %% a % relief is generally >3 m; in some places 40 m. In some places, deposits include 1:100,000. caa g the surface. Contains local thin, discontinuous beds, lenses, or stringers of sand or l %% lca e lss kg glaciotectonically-folded and ice-thrust masses of bedrock (see symbol IT). Map Lopez, D.A., 2000c, Geologic map of the Chester 30’ x 60’ quadrangle, north-central Montana: wla %% lss fine gravel; pockets or pods of iceberg-rafted granules and pebbles, or isolated lss lu lca C % %% unit includes collapsed glacial sediment (till and flowtill), collapsed supraglacial Montana Bureau of Mines and Geology Open-file Report MBMG 445, 10 p., map scale lu r Limit of Illinoian glaciation on the Sweet Grass Hills e lu % rafted erratic cobbles or boulders. Interbedded with sand, fine gravel, till, or lu e

k % lake clay, silt, and sand, and outwash and ice-contact sand and gravel. Glacial, 1:100,000. caa flowtill in some places; some rare ice-rafted masses (clasts) of till are 1–2 m in R 1000 lu R caa glaciolacustrine, glaciofluvial, and alluvial sediments were redeposited by mass Lopez, D.A., 2002, Geologic map of the Lonesome Lake 30’ x 60’ quadrangle, north-central lu % diameter. Graded beds, silt blebs and nodules, or rip-up clasts of till or lake silt lu R al lu %% lu movement (flow and sliding) as a result of melting of buried ice long after initial Montana: Montana Bureau of Mines and Geology Open-file Report MBMG 446, 12 p., lu tlx(e) %% %% Limit of a late Wisconsin glacial readvance, or position of and clay are present locally. Strongly contorted, with slump structures, load k

wla R e gg deglaciation. In some places, boundaries between stagnation-moraine deposits and map scale 1:100,000. e lu r % a significant stillstand of an ice margin—Ticks are on the structures, and folds, in some places. Generally not faulted. Dessication cracks lss caa lss C ground-moraine or end-moraine deposits are transitional and contacts are arbitrary. Mickelson, D.M., Clayton, Lee, Fullerton, D.S., and Borns, H.W., 1983, The late Wisconsin al % % lse % %% % R e % are common in some places. Commonly oxidized in upper 1–2 m; local iron oxide l %% % % side of the advance Thickness 4–20 m, locally 40 m lss lu tlx i %% % glacial record of the Laurentide ice sheet in the United States, in Porter, S.C., ed., caa lca M stains. Soft to very firm; cohesive and compact. Very plastic and sticky when lu gg lu R % lu Late-Quaternary environments of the United States, volume 1, the late Pleistocene: lu n lss lu caa gg e % moist; hard when dry. Locally gritty. Dry clay and silt commonly breaks into tlx lu te Inferred limit of a glacial readvance marked by the distal margin ke KAME-MORAINE DEPOSITS—Ice-contact gravel, sand, and minor silt similar to Minneapolis, University of Minnesota Press, p. 3–37.

tlx Tiber r

%

u % % tlx R % chips or blocks. Clay minerals are dominantly montmorillonite. Selenite lu o % deposits in map unit kg. Description of map unit kg applies. Comprises segments Montagne, Clifford, Munn, L.C., Nielsen, G.A., Rogers, J.W., and Hunter, H.E., 1982, Soils of cad Reservoir lu F % of glaciotectonic deposits or glaciotectonic structures wla lss lca (gypsum) crystals <6 mm in length are present locally in fractures and are gg R lss % lse % of end moraines; gently to steeply sloping ridges or aligned hummocks and hills Montana: Montana Agricultural Experiment Station Bulletin 744, 95 p. % %% % abundant in saline lake sediment. Secondary calcium carbonate concretions tlx lu lu kg Box Elder Marginal end moraine—Single till ridge formed along the margin of an ice lobe (kames) of sand and gravel. Relief is generally 4–10 m. Kame moraine deposits in Simonson, G.H., Rogers, J.W., Brownfield, S.H., Richardson, R.E., and Nielsen, G.A., 1978, lu lss % locally are present in upper part. Gullies are common in some places. Deposit is lu kg % % % some places are replaced laterally by till end-moraine deposits that are included in General soil map of Montana: Montana Agricultural Experiment Station Miscellaneous %% susceptible to landslide processes (chiefly slump) in exposures (see map unit jea). gg lu lu lse % the map unit. Thickness 4–l5 m, locally >20 m Publication 16, scale 1:1,000,000. lu lu % % gg Most deposits are off-shore deposits of former lakes. Present beneath flat plains % % cad % Smith, J.F., Jr., Witkind, I.J., and Trimble, D.E., 1959, Geology of the lower Marias River area, tlx % % kg Broad till ridge formed at the junction of two ice lobes and in small basins formerly occupied by glacial and postglacial lakes and ponds. IT lu gg % % Du Interlobate moraine— lca lss lu ck kg ICE-CONTACT SAND AND GRAVEL—Deposited on or against glacial ice; Choteau, Hill, and Liberty Counties, Montana: U.S. Geological Survey Bulletin % % lss C south of East Butte of the Sweet Grass Hills Flat to hummocky surface topography. Thin and discontinuous in some areas. lu cad % re sediment collapsed when ice subsequently melted. Pale-yellow, brownish-yellow, 1071-E, p. 121–155. % % e R ldb r tlx lu kg % % %% k Overlapped by flood-plain alluvium adjacent to some streams. Includes lake silt ive tlx grayish-yellow, reddish-brown, yellowish-brown, olive-brown, grayish-brown, Soller, D.R., 1993, Preliminary map showing the thickness and character of Quaternary R lu caa lu cad s % lse lse Lonesome Mostly till. Most of the ridges delineate the configurations of vanished and sand where lake clay, silt, and sand have not been distinguished. Includes a % Minor moraines— i Lake lss brown, olive, yellowish-gray, olive-gray, brownish-gray, gray, or mottled, deposits in the United States east of the Rocky Mountains: U.S. Geological Survey r lu some till with a thin veneer of silt and clay. Includes some ice-contact and a gg % cad ice margins. Local relief of ridges typically is 2–10 m. Includes "annual moraines," calcareous sand and gravel and minor silt. Textures vary abruptly, laterally and Open-File Report 93-543, scale 1:3,500,000. M lu lca % % kg outwash sand and gravel, small lake delta deposits, and bedrock outcrops. In some k lu R caa "washboard moraines," "small moraines," "corrugated moraines," and "transverse ridges" r lu lu lu vertically. Locally, map unit is dominantly boulder or cobble gravel; in some Soller, D.R., 1994, Map showing the thickness and character of Quaternary sediments in the o al places, lake clay and silt are overlain by eolian silt and sand, sheetwash alluvium, F tlx gg places, pebbly silt and fine sand. Sand and gravel commonly are interbedded with glaciated United States east of the Rocky Mountains-Northern Plains states (west of y lca lca r lss lse alluvial-fan deposits, or flood-plain alluvium. Thickness 1–5 m, locally >15 m D cad tlx or contain lenses, inclusions, or clasts of clay, silt, till, or flowtill. Poorly to well 102° West Longitude): U.S. Geological Survey Miscellaneous Investigations Series

gg tlx r al e

%

tlx Ma v %

% % stratified; poorly to moderately sorted. Irregularly bedded to well bedded; beds are Map I-1970-D, scale 1:1,000,000.

% gg r i % Ice-margin alignment interpreted from ice-margin drainage channels and

tlx lu lu i as R lss LAKE SAND AND SILT—Grayish-yellow, yellowish-brown, grayish-brown, brown,

%

% discontinuous laterally. Faults, folds, and slump and collapse structures are Swenson, F.A., 1957, Geology and ground-water resources of the Lower Marias Irrigation %

gg lu cad % till ridges yellowish-gray, olive-gray, brownish-gray, gray, or mottled, calcareous silt and % %

%

lu % common. Gravel locally is cemented by iron oxides or secondary calcium Project, Montana [with a section on chemical quality of the ground water by H.A.

% caa %

kg lu lu tlx(e) %% sand mixed with minor clay and gravel. Generally well stratified and well sorted. % % tlx lu gg tlx lu lca lss % carbonate in zones; intense iron-oxide stains on some clasts. Clasts are subrounded Swenson]: U.S. Geological Survey Water-Supply Paper 1460-B, p. 41–98.

kg lu Ice-molded or ice-scoured landform—Linear drumlin, rock drumlin, or fluting. Long Typically horizontally-bedded or massive, fine or medium sand containing

%

%% % % to well rounded; clast composition is similar to that of associated till. Typically, Tuck, L.K., 1993, Reconnaissance of geology and water resources along the north flank of the %

lu %% % %

% scattered granules or small pebbles. Commonly interbedded or intercalated with lca %% axis of symbol is parallel to the direction of ice movement. Some symbols represent more than % % shale clasts are much less abundant than in associated till; resistant erratic clasts are Sweet Grass Hills, north-central Montana: U.S. Geological Survey Water-Resources %%

%% massive, bedded or laminated, silt containing dropstones; in some areas, chiefly

% lu % %

lu al % one landform more abundant. In some places, includes blocks (clasts) of redeposited till. Investigation Report 93-4026, 68 p.

% lca caa %

lu lu al laminated silt and fine sand. Commonly slumped and contorted on hillslopes. % % Fragments of lignite (bedrock) are ubiquitous in many places. Surfaces are flat to U.S. Department of Agriculture, unpublished soils maps of Toole, Liberty, Hill, Blaine, lu lca % Detrital fragments of lignite (bedrock) are abundant in many areas, concentrated in lu Big Sandy undulating or hummocky to knobby. In some areas deposits form isolated mounds Pondera, Choteau, and Phillips Counties, Montana, provided by Robert Lund, Montana Conrad lca lse Esker—Subglacial or englacial stream deposit sand crossbeds. Clasts are chiefly subrounded and rounded erratic limestone, lu % tlx(e) tlx %% %% or irregular hills. Commonly pitted with shallow ice-block depressions (kettles). Geospatial Center, Bozeman, Montana. %% tlx tlx ke caa

R lu lse dolomite, and igneous and metamorphic rocks that were ice rafted or reworked %

% Boulder litters are present locally on the surface. Local relief is generally 3–15 m, Veseth, Roger, and Montagne, Clifford, 1980, Geologic parent materials of Montana soils: lu lss tlx from till. Present beneath lake plains and in small basins formerly occupied by % lda lu Buried bedrock valleys of the ancestral Marias and Missouri Rivers— locally >20 m. In some places, deposits were modified by waves and currents in Montana Agricultural Experiment Station Bulletin 721, 117 p.

% % caa caa A middle Pleistocene fill deposit is present in the subsurface in the buried valleys. It is glacial and postglacial lakes. Local relief 2–4 m. Includes some lake clay and lda Lees Lake % % % lse lakes; the ice-contact deposits are overlain by thin, discontinuous, lake clay, silt, lu tlx lss % caa % lca not well exposed in the Shelby quadrangle, but it is well exposed in the adjacent Havre silt, flood-plain and channel alluvium, and till. In many areas, overlies lake clay caa Big sand, and gravel. Distinguished from kame-moraine deposits (map unit ke) lda lu % Sa

lu % lca % n quadrangle in the vicinity of Havre (Fullerton and others, 2012). The alluvial and lacustrine and silt. Thickness 1–8 m, locally >10 m % % %

caa % d arbitrarily in some areas. Includes some kame-moraine deposits, kame-delta

%

lu % y

%

al lca lca % fill deposit commonly includes, from younger to older: glacial lake sediment of Illinoian age;

cad lu C deposits, and lake-delta deposits. Also includes some outwash sand and gravel,

%

lu % lu

% % r LAKE CLAY, SILT, SAND, AND GRAVEL—Undivided deposit of lake clay, silt, % % e

%

lss lu % ek nonglacial overbank and channel alluvium and pond or lake deposits of pre-Illinoian age; and lake clay, silt, and sand, inset flood-plain and channel alluvium, till, and bedrock

% tlx lca % glacial lake deposits of pre-Illinoian age. The fill deposits are overlain by eolian deposits, sand, and fine gravel. Overlain by eolian sand and silt in some places. Includes lca cad outcrops. Locally overlain by till or flowtill; in some areas overlain by eolian silt

lca lca channel and flood-plain alluvium, sheetwash alluvium, lake deposits, and till units of late inset and overlapping flood-plain and channel alluvium. Descriptions of lake

% %

%

% % lca % and sand. Thickness 1–10 m, locally >15 m

% lu %

lca lu % R % Wisconsin and Illinoian age (informal Fort Assiniboine and Herron Park tills, respectively, of deposits in map units lca and lss apply. Thickness 1–3 m, locally >10 m %

tlx lca % % % lu % lca % % %% % Fullerton and Colton, 1986). The fill deposits overlie till of pre-Illinoian age (upper unit of gg OUTWASH SAND AND GRAVEL—Sediment deposited in subaerial meltwater tlx(s) lu %

ldb % % informal Havre till of Fullerton and Colton, 1986); lake and fluvial deposits; a paleosol in the lse LAKE AND EOLIAN SAND AND SILT—Complex map unit of lake sand and silt

% tlx % lse % streams. Pale-yellow, brownish-yellow, grayish-yellow, reddish-brown,

tlx % % lower unit of Havre till; glacial lake deposits; and nonglacial fluvial gravel from the mountains and eolian sand and silt. Lake deposits in many places were reworked by wind and

% %

% % % tlx

% yellowish-brown, olive-brown, grayish-brown, brown, olive, yellowish-gray, % % %

lu tlx % lu tlx % % %% % to the south and west. The basal nonglacial gravel beneath the fill deposits contains Irvingtonian are overlain by eolian deposits % R % %

% % brownish-gray, olive-gray, gray, or mottled, calcareous sand, pebbly sand, and

% % %

%

% % lse % vertebrate fossils; the fill contains rare vertebrate (ungulate) fossils Eolian sand and silt—Yellow, yellowish-brown, olive-brown, grayish-brown, brown, % lu % caa caa % gravel; locally pebbly sand and silt. Poorly to well stratified; poorly to well sorted. % brownish-gray, gray, or mottled windblown sand and silt in blanket-like deposits; 0 lu c I RIVE a 100 R R Stratification typically (1) horizontal beds of well-sorted sand, (2) pebbly sand with

% a OU

% lu 000 ISS local low dunes. Calcareous. Well stratified; poorly sorted to well sorted. tlx 1 % R M ripple-drift, cut-and-fill, planar, or trough crossbeds, or (3) interbedded pebbly sand tlx(s) Brady S Typically loose, homogeneous, massive, fine sand and silt with faint beds or R k % and pebble, cobble, or boulder gravel. Local lenses or beds of silt and clay; local it caa lss tlx(s) lu lca lu C gg wla R cross-beds. Very friable; weakly compact; slightly hard; subangular blocky tlx lss r tlx e %% boulder beds; local blocks (clasts) of till or masses of flowtill. Clasts are e cad structure; not sticky or plastic when moist. Generally clast free. Contains cad k %% R lss tlx subangular to very well rounded; diameter of largest clasts generally decreases in IT tlx caa caa tlx lu al discontinuous accumulations of secondary calcium carbonate in some places; al lu caa caa lu % R downstream direction in valley train deposits. Clast composition generally is 48°00' tlx lca R % kg tlx R stained by iron oxides locally. Typically oxidized throughout. In some places, kg lu 48°00' similar to that in local till; locally dominantly shale or dominantly redeposited 112°00' 110°00' contains root casts and weakly developed buried soils (humic horizons). Mostly quartzite, argillite, chert, and chert conglomerate derived from older gravel. stable, with grass cover; local blowouts. Undulating or rolling topography. Geology compiled in 1976–86, 1990–2002, 2004–2010 Boulders and large cobbles are chiefly subangular or subrounded, reworked, glacial Base hydrology from U.S. Geological Survey, 1955 SCALE 1: 250 000 Thickness 0.5–3 m; maximum 6 m Edit and digital layout by Jeffery R. Hartley erratics (limestone, dolomite, granite, pegmatite, gneiss, schist, diorite, and other Base topography from National Elevation Dataset (NED), U.S. Geological Survey 1974 (http://seamless.usgs.gov) Lake sand and silt—Similar to deposits in map unit lss Geology digitized by Charles A. Bush igneous and metamorphic rocks). Fragments of lignite (bedrock) are ubiquitous in Base cities, roads, and railroads from Montana State Library 2011 (http://nris.mt.gov) 5 0 5 10 15 MILES 2 1 many areas. Clasts in some places are intensely stained by iron oxides or Digital cartography by Charles A. Bush cad COLLUVIUM, SHEETWASH ALLUVIUM, LAKE DEPOSITS, AND manganese oxides; gravel is locally cemented by secondary calcium carbonate. Published by U.S.Geological Survey Science Publishing Network Denver GLACIOFLUVIAL DEPOSITS—Complex map unit in abandoned meltwater TRANSVERSE MERCATOR PROJECTION Surfaces are smooth, undulating, or gently rolling. Local relief is 1–5 m. Includes Manuscript approved for publication July 27, 2012 channels and glacial lake outlet sluiceways. Channel sides are sharply defined to 1927 North American Datum 5 0 5 10 15 20 KILOMETERS some till, ice-contact sand and gravel, lake-delta deposits, inset flood-plain and indistinct. Some of the channels and sluiceways are shallow, broad flats. In some channel alluvium, and bedrock outcrops. In some areas, deposits were modified by places, lake deposits are overlain by eolian sand and silt. Locally, glaciofluvial waves and currents in lakes, and outwash sand and gravel is overlain by lake clay, gravel and sand deposited by meltwater streams underlies the lake and alluvial CONTOUR INTERVAL 100 METERS silt, and sand. Locally overlain by eolian silt and sand. Thickness 1–4 m, locally deposits. Valley sides are chiefly colluvium, sheetwash alluvium, till, lake C A N A D A 104° >10 m ° 106° 1955 MAGNETIC DECLINATION FROM TRUE NORTH VARIES FROM 19¾° EASTERLY FOR deposits, and bedrock outcrops. Isolated large boulders or lag deposits of cobbles 118° 116° 114° 112° 110° 108 49° CORRELATION OF MAP UNITS Some of the sand and gravel mapped as outwash deposits possibly is early 49° THE CENTER OF THE WEST EDGE TO 18½° EASTERLY FOR THE CENTER OF THE EAST and boulders are present on valley sides in some places. Gullies locally are postglacial alluvium. Precipitation and runoff likely were greater than at present M O N T A N A EDGE. ANNUAL CHANGE IS 0°40’ WESTERLY common on valley sides. Channel alluvium is inset into other deposits; flood-plain INT OW WOLF PO for several thousand years after initial deglaciation, and glacial, ice-contact, SANDPOINT K SHELBY HAVRE GLASG deposits overlap some lake deposits. Sheetwash alluvium locally overlaps other ALISPELL CUT BANK 48° glaciofluvial, and glaciolacustrine sediments were eroded and redeposited as 48° deposits on valley sides; in some places it mantles much of the fill on the valley GLACIOFLUVIAL alluvial fills. The surface morphology, clast composition, and sedimentary DIVE DEPOSITS floor. Distinction of map units cad and caa is arbitrary in some areas. Combined RDAN GLEN NOTE: structures of the deglacial outwash and early postglacial alluvium are similar, and SPOKANE WALLACE CHOTEAU GREAT FALLS LEWISTOWN JO thickness of deposits is 1–10 m, locally >15 m 47° This map was prepared to serve as a database for compilation of a Quaternary geologic map of the Lethbridge 4° x 6° quadrangle, LANDSLIDE the deposits have not been distinguished on published maps BEDROCK Colluvium—Similar to map unit caa. Thickness 0.5–8 m 47° United States and Canada (scale 1:1,000,000). Letter symbols for the map units are those used for the same units in the Quaternary GLACIAL ICE-CONTACT ALLUVIAL LACUSTRINE DEPOSITS COLLUVIAL DEPOSITS DEPOSITS DEPOSITS DEPOSITS DEPOSITS Sheetwash alluvium—Similar to map unit wla. Thickness 0.5–4 m lda WHITE MILES CITY Geologic Atlas of the United States map series. This map is a simplified compilation of data from many sources, listed in SOURCES OF LAKE DENSITY-CURRENT UNDERFLOW-FAN DEPOSITS—Pale-yellow, H ROUNDUP FORSYTH AMILTON BUTTE SULPHUR INFORMATION, at several map scales. Some of the map data are simplified and generalized. For example, small areas of pediment, 2 1 grayish-yellow, yellowish-brown, brown, brownish-gray, olive-gray, gray, or SPRINGS 46° caa COLLUVIUM, SHEETWASH ALLUVIUM, AND LANDSLIDE alluvial-fan, and terrace deposits (map unit pgd) that were mapped separately at larger scales by others, here are combined as single mottled, calcareous silt, sand, and gravel. Well stratified; generally well sorted. 46° DEPOSITS—Complex map unit on valley sides and eroded uplands. Includes polygons. Many surficial deposits that can be shown accurately as small polygons at 1:250,000 scale are omitted here because they are Holocene Chiefly laminated silt and very fine sand interbedded with thin layers of clay or EKALAKA afj wla areas of lag sand and gravel over till and (or) bedrock; alluvial-fan and HARDIN too small to be shown at 1:1,000,000 scale. al fine to coarse sand. Average grain size decreases from top to bottom. Foreset beds ELK CITY DILLON BOZEMAN BILLINGS sheetwash-alluvium fan or apron deposits at bases of hillslopes and at mouths of 45° Map units are surficial deposits and materials, not landforms. The deposits that comprise some constructional landforms (e.g., are absent; basal sediments commonly are lake clay and silt, but they are not delta 45° ? lca lss lu lse cad caa cly crr gullies; lag boulder and cobble accumulations; sheet-wash-eroded or ground-moraine deposits, end-moraine deposits, and stagnation-moraine deposits, all composed of till), are distinguished for purposes of bottomset beds. Silt and sand are crossbedded or horizontally bedded; ripple-drift tlx tlx stream-eroded till or bedrock dissected by gullies; extensive areas of bedrock I D A reconstruction of glacial history. Deposits and materials are distinguished on the basis of genesis, lithology or composition, texture or LATE WISCONSIN tlx ke kg gg lda ldb lamination is common. Clasts are mixed rocks derived from surficial deposits and H O WYOMING (e) (s) jea late outcrop DUBOIS ASHTON 44° particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or bedrock that were eroded, transported, and deposited by catastrophic-flood 44° Pleistocene Colluvium—Yellowish-brown, olive-brown, brown, olive, yellowish-gray, 104° agronomy. Rather, it is a generalized map of soils as recognized in engineering geology, or of substrata or parent materials in which QUATERNARY drainage into a glacial lake. Mapped at several localities east of Conrad. 118 106° brownish-gray, gray, or mottled debris transported and deposited by ° 116° 114° 112° 110° 108° pedologic or agronomic soils are formed. Thickness 3–>10 m Pleistocene mass-movement processes. Calcareous or noncalcareous. Loose to compact. Nonstratified or faintly stratified; nonsorted or poorly sorted. Commonly massive. pgd middle ldb DELTA SAND AND GRAVEL—Brownish-yellow, yellowish-brown, olive-brown, INDEX TO 1:250,000 TOPOGRAPHIC QUADRANGLES Where derived from local bedrock, colluvium typically is angular and subangular grayish-brown, brown, olive, brownish-gray, olive-gray, gray, or mottled, Showing location of the Shelby 1° x 2° quadrangle in red Pleistocene blocks, boulders, cobbles, pebbles, and granules of local bedrock in a clayey to ? ? ? calcareous clay, silt, sand, and gravel. Moderately or well stratified; moderately or sandy matrix. Where derived from sand and gravel, typically it is sand or pebbly early well sorted. Bottomset beds generally are absent. Foreset beds are sand. Where derived from glacial drift, typically it is boulders, cobbles, pebbles, Pleistocene ripple-laminated or planar-bedded, coarse to fine sand and silt and well-sorted sand and granules of erratic limestone and dolomite, erratic igneous and metamorphic and gravel. Topset beds are (1) well-sorted coarse sand and gravel, (2) Pliocene rocks, and local sandstone and shale in a clayey to sandy matrix. Three or more ? moderately-well sorted gravelly sand, or (3) planar-bedded, trough-crossbedded, or buried soils (humic horizons) locally are present in the colluvium; lignite (bedrock) TERTIARY ripple-laminated fine or medium sand. Grain size of sediment in topset beds varies fragments are ubiquitous in many areas. Thickness 0.5–5 m abruptly, laterally and vertically. Cobbles and boulders are common. Clasts are 114° 102° Sheetwash alluvium—Similar to map unit wla 50° EXPLANATION chiefly subangular; clast composition is chiefly local bedrock because the delta 112° 104° R Landslide deposits—Similar to map unit jea 110° 108° 106° Osage formed at the mouth of a lake spillway channel that was deeply incised into LW bedrock. Mapped only in the southwest corner of the quadrangle. Some small Kincorth Ardill Galilee MOUNTAIN VALLEY AND PIEDMONT GLACIATION Monarch Bow Island Maple Creek Neville HOLOCENE, LATE PLEISTOCENE, AND MIDDLE PLEISTOCENE Hills an R er Kipp Oldm iv Ettington Dummer Yellow Grass delta deposits are included in lake silt and sand (lss) and undivided lake deposits C2 Riv er Taber 2 Porcupine n PT ma Pinedale till cly LOAMY COLLUVIUM —Ownish-orange, yellowish-brown, orange-brown, d Lethbridge Robinson (lu). Thickness 3–10 m l Fort Macleod r Crane Valley Stoughton O e v LW Weyburn olive-brown, grayish-brown, brown, brownish-yellow, yellowish-gray, olive-gray, i s Kincaid R r ill Brocket r e H Lafleche LAURENTIDE CONTINENTAL GLACIATION e y iv Shaunavon brownish-gray, gray, or mottled loam and sandy loam in the Sweet Grass Hills. iv l IL Pincher l R Cypress PLEISTOCENE AND PLIOCENE R e y ton r LW Calcareous or noncalcareous. Nonstratified or weakly stratified; nonsorted or er B a Raymond Foremost LW LW Late Wisconsin till pgd t M Magrath Etzikom Pakowki Eastend Hardy Radville PEDIMENT, ALLUVIAL-FAN, AND FLUVIAL-TERRACE DEPOSITS— White, a t IL Viceroy Drywood W in poorly sorted. Generally pebbly or cobbly. In most places, clasts are angular and a Spring Coulee Ravenscrag S Battle Creek WHITEWATER Bengough IL Illinoian till pink, reddish-yellow, yellow, yellowish-brown, reddish-brown, orange-brown, C Raley subangular local bedrock: chiefly intrusive igneous rocks (syenite, syenite 2 LOBE Twin Valley M ISSOURI Frobisher olive-brown, brown, brownish-yellow, yellowish-gray, olive-gray, brownish-gray, Cardston AN Summercove PW A Wood Mountain Isolated and scattered exposures of porphyry, and minor trachyte porphyry, diorite porphyry, and monzonite porphyry)

T Waterton Lakes W Reliance Milk River R E Val Marie Torquay Estevan pre-Wisconsin till and glacial erratic boulders gray, or mottled gravel, sand, and silt. Calcareous or non-calcareous. Poorly to E Upland National Park Mountain View Lethbridge Outram and sedimentary rocks (sandstone, mudstone, shale, and minor limestone). Glacial Mi B Rangeview Climax Lake Alma lk L Waterton Park River Comrey TCH IL Ratcliffe EWAN PI Pre-Illinoian till on north margin moderately well stratified; poorly to moderately well sorted. Boulders, cobbles, A H 49° Kimball Del Bonita A Orkney Killdeer Coronach Big Beaver Weyburn SASKATC K erratics from Canada are present in some places on the margins of the Sweet Grass Twin River ALBERTA Foremost Divide of Bearpaw Mountains Glacier Rosefield Willow Bunch Lake COTEAU DAKOTA pebbles, and granules in a sand and silt matrix. Clasts in pediment and alluvial-fan Pinhorn AS IL Big Muddy NORTH Hills. Includes some landslide deposits, flood-plain and channel alluvium, National S Willow Creek Cypress Lake CANADA Wood Mountain GB Scattered glacial erratic boulders, no till Hall Coulee MONTANA deposits are chiefly subangular; clasts in fluvial-terrace deposits are subangular, Park Babb Fortuna pediment, alluvial-fan and alluvial-terrace deposits, and extensive bedrock S UNITED STATES Crosby Bowbells PT Sunburst w Pe Glacial lakes Great Falls and Musselshell. subrounded, or rounded. Clast lithologies are chiefly syenite, syenite porphyry, IL ee Opheim outcrops. Thickness 0.5–>6 m; maximum >15 m t e GB Flaxville Full extent of lakes not shown G Turner r trachyte porphyry, diorite porphyry, monzonite porphyry, sandstone, and shale. R l Plentywood ras HAVRE LOBE e Cu nk Cre s H IL Whitewater s Scobey Not glaciated o t Ba e ills s k Peerless Fluvial deposits are present beneath multiple terrace surfaces on the Sweet Grass

Grenora crr ck Boundary FROST-RUBBLE AND TALUS-RUBBLE DEPOSITS—Blocks, slabs, flagstones, Cut Bank Fresno Flaxville

Browning Alamo Hills; at least three surfaces are older than the late Wisconsin till. Till deposited Plateau SHELBY LOBE Reservoir Chinook P Plain LAURENTIDE CONTINENTAL GLACIATION l channers, boulders, and cobbles produced primarily by frost riving of trachyte West Glacier a y Ma IL t during at least two pre-Wisconsin glaciations overlies buried pediment, alluvial Two Medicine r e Lostwood ia Chester M P Medicine Lake s R Shelby Havre Harlem ilk a o Late Wisconsin porphyry, syenite porphyry, and syenite, and mass-movement of frost rubble. Most East Glacier Park lobe ive River u p White Earth r l fan, and terrace deposits in the subsurface; however, only the late Wisconsin M Marias Pass Lake ar Ray PT Limit of late Wisconsin glaciation (LW), of the rubble is interpreted to have been formed in a periglacial environment when Frances Dodson Bowdoin Ri surface till is mapped. Includes some colluvium, sheetwash alluvium, eolian silt ou ve defined by stratigraphy and (or) surface Valier r the Sweet Grass Hills were surrounded by glacial ice. Rubble is nonstratified and Tiber Reservoir Box Elder Hinsdale Malta IL morphology and sand, and bedrock outcrops. Thickness generally 1–4 m, locally >10 m n Rocky Boy Late Wisconsin Williston nonsorted; little or no matrix. Includes landslide deposits, rock-fall and rock-slide Conrad LW Big Sandy PI LW Glasgow Lake Sakakawea t Bearpaw phase of glacial Brockton Culbertson Limit of "C2" glacial readvance in southwestern Alberta deposits, talus-flow and debris-flow deposits, colluvium, and bedrock outcrops. 48° a Cut Bank Pendroy Poplar Mountains MALTA SUBLOBE Lake Jordan Mi Williston PRE-QUATERNARY i Shelby Frazer Wolf Point sso Thickness generally >1 m; locally >10 m n LOMA SUBLOBE (792 m; 2,600 ft) ur Limit of a regional glacial readvance caused Havre Lodge Pole Fort Peck Wolf Point i River Keene R BEDROCK s Bynum Glasgow by reorganization of glacial dispersal centers; IL Eagleton T iver Little Rocky Mts GLASGOW OR defined by stratigraphy and surface morphology. eton R Sun Prairie Cartwright Landusky Fort Peck LW Watford City Hachures on the "up-glacier" side of limit HOLOCENE AND PLEISTOCENE Choteau Fort Benton Reservoir MISSOURI VALLEY Iliad uri River IL YELLOWSTONE jea SLUMP-BLOCK LANDSLIDE DEPOSITS AND ROCKSLIDE DEPOSITS— 1 sso LOBE Illinoian Sheetwash alluvium, for purposes of this map, is material that was transported and deposited by unconfined Power Mi Sidney LOBE

r Mapped only in the Sweet Grass Hills. Most of the individual landslide deposits running water, chiefly sheet flow and rill wash. e IL v Limit of Illinoian glaciation (IL), defined by stratigraphy 2 Portage Richey i PT R elsewhere in the quadrangle are too small to map at this scale. Slump-block Colluvium, for purposes of this map, is material that was transported and deposited by slow

Killdeer and (or) surface morphology e

L Augusta r Mountains landslide deposits are masses of bedrock and unconsolidated materials that rotated mass-movement processes, chiefly creep. Great Falls on e t i t Pre-Wisconsin Highwood v IL s t Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement i l Grassy Butte Dunn Center e or slid downslope as a unit, with little or no flow. The physical properties of the R ow Mountains Circle M Limit of pre-Wisconsin till and glacial by the U.S. Government. h ll M e it Y TA i Golden Valley s erratic boulders (limit of PW). Till is not present transported materials are not greatly altered; original textures, stratification,

d us O so Late Wisconsin phase Denton u Roy PW Cascade J Valentine Jordan Intake r s u as far south as the limit of boulders e Late Wisconsin phase of AK

A bedding, and other sedimentary structures of slumped materials are disturbed but of glacial Lake Great Falls e v r LW Although this information product, for the most part, is in the public domain, it also contains copyrighted

i l D i s N

R glacial Lake Musselshell (1142 m; 3,715 ft) H R h

i A T Pre-Illinoian Pleistocene e retained. Toes of some deposits form sub-parallel, arcuate, concentric, hummocky materials as noted in the text. Permission to reproduce copyrighted items must be secured from the r (792 m; 2,600 ft) confluent i

u l v RT Choteau o l Glendive N 47° e Watford City

s O R with glacial Lake Jordan is r ridges, separated by elongate swales. Clasts in rockslide deposits are granules to copyright owner.

N Southern limit of known surface exposures of

i M Grea endive MO t Falls Lewistown v Gl Lewistown e Jordan pre-Illinoian Pleistocene till (limit of PI) on r slabs and blocks; some blocks are >3 m in diameter; some deposits are jumbled north flank of Bearpaw Mountains blocks. Most of the mapped deposits are stabilized by vegetation. Includes This database, identified as OFR 2012–1170, has been approved for release and publication by the U.S. Geological Survey (USGS). Although this database has been subjected to rigorous review and is Limit of glacial erratic boulders on bedrock colluvium, frost-rubble and talus-rubble deposits, sheetwash alluvium, and bedrock 25 0 25 50 75 100 MILES erosion surfaces (limit of GB) substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and outcrops. Thickness 3–5 m, locally >10m Location of Shelby quadrangle review. Furthermore, it is released on condition that neither the USGS nor the U.S. Government may be 25 0 25 50 75 100 KILOMETERS held liable for any damages resulting from its authorized or unauthorized use. Generalized direction of ice flow River, stream, and modern lake shoreline Publishing support provided by: Figure 1. Regional ice flow during maximum Denver Publishing Service Center late Wisconsin glaciation. Manuscript approved for publication July 27, 2012 For more information concerning this publication, contact: Center Director, USGS Geology and Environmental Change Science Center Box 25046, Mail Stop 980 (303)236-5344 QUATERNARY GEOLOGIC MAP OF THE SHELBY 1° × 2° QUADRANGLE, MONTANA Or visit the Geology and Environmental Change Science Center Web site at: http://esp.cr.usgs.gov/ For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, By 1–888–ASK–USGS Digital files available at http://pubs.usgs.gov/of/2012/1170 David S. Fullerton, Roger B. Colton, and Charles A. Bush Suggested Citation: Fullerton, D.S., Colton, R.B., and Bush, C.A., 2013, Quaternary geologic map of the Shelby 1˚ x 2˚ quadrangle, Montana: U.S. Geological Survey Open-File Report 2012–1170, scale 1:250,000 2013 [http://pubs.usgs.gov/of/2012/1170].