U.S. DEPARTMENT OF THE INTERIOR SCIENTIFIC INVESTIGATIONS MAP 2843 U.S. GEOLOGICAL SURVEY Pamphlet accompanies map

114˚ 102˚ 50˚ 50˚ EXPLANATION 112˚ 104˚ VALLEY GLACIAL DEPOSITS Osage 110˚ 106˚ LP 108˚ Late Pinedale till

S Kincorth Galilee ILL Neville Ardill MP Middle Pinedale till H Monarch PINE iver Bow Island Maple Creek U n R EP Early Pinedale till C dma R Dummer Kipp Ol Ettington PO Taber Yellow Grass C2 ver LB Ri Late Bull Lake till n a Fort Macleod Lethbridge Robinson Crane Valley Stoughton EB Early Bull Lake till Oldm lly River Be Weyburn BL Bull Lake till, undivided LW Lafleche Kincaid KD Kennedy drift Brocket CYPRESS HILLS Shaunavon r Pincher ve Ri CYPRESS HILLS PIEDMONT GLACIATION GLACIAL DEPOSITS ver Ri ary (OUTLET DEPOSITS OF GLACIERS FROM THE ton LW er M Raymond NORTHERN MONTANA ICE FIELD) t Hardy Wat n Foremost 2 Etzikom Eastend Radville ai Magrath LW C P3 S Ravenscrag Viceroy Pinedale 3 till Drywood Pakowki Battle Creek Spring Coulee Bengough P2 Pinedale 2 till r VMR C2 Raley B P1 Pinedale 1 till WATERTON Rive Twin Valley Frobisher LAKES Summercove elly Cardston CONTINENTAL GLACIAL DEPOSITS NATIONAL B Reliance 2 PARK C GB Estevan LW Late Wisconsin till Waterton Val Marie Mountain View Torquay Outram Park Milk River Milk Ri Rangeview Climax Lake Alma IL Illinoian till Kimball ver Comrey IL Ratcliffe 49˚ MBS Del Bonita Divide Orkney Coronach 49˚ PW Pre-Wisconsin till and glacial erratic boulders Big Beaver Twin River ALBERTA Killdeer MP PI GLACIER BL IL SWEETGRASS HILLS Rosefield Pre-Illinoian till (Pleistocene) Pinhorn SASKATCHEWAN Big Muddy NATIONAL LIMIT OF MAJOR LP BL Hall Coulee GB Pre-Illinoian glacial erratic boulders on eroded bedrock PARK EP Willow Creek ICE-MARGIN READVANCE ver Ri CANADA (Pleistocene)—Contains no till Babb LB Milk Fortuna Crosby UNITED STATES MP Bowbells EB VALLEY GLACIATION Sunburst IL IL Opheim GB Limit of late or middle Pinedale glacial advance (limit of PEERLESS PLA GB SMRS Turner unit LP or MP) Flaxville Plentywood LP KD MRRS Peerless FLAXVILLE Limit of early Pinedale glacial advance or glaciation (limit of Cr. ank Whitewater Scobey PLAIN unit EP) Cut B Fresno LIMIT OF ICE-MARGIN Limit of late Bull Lake glacial advance or glaciation (limit of MP T Cut Bank Reservoir BOUNDARY READVANCE OR POSITION OF EAU Grenora unit LB) BURIED LIMIT ICE-MARGIN STILLSTAND Browning PLATEAU Alamo West Glacier TMRS GS OF ILLINOIAN Limit of early Bull Lake glacial advance or glaciation (limit GLACIATION of unit EB), or limit of Bull Lake till, undivided (unit BL) LP Chinook BVMR Lostwood IL Mapped limit of pre-Bull Lake Kennedy drift (limit of unit East Glacier Park Chester Po Medicine Lake P2 P1 Shelby Havre p KD) M la Harlem il r k BVYR P3 R iver R White Earth iver PIEDMONT GLACIATION Ray Marias Pass Lake Tiber Limit of Pinedale 3 or Pinedale 2 glacial advance (limit of Frances Reservoir BVMR Valier Dodson Bowdoin unit P3 or P2) Box Elder Hinsdale Limit of Pinedale 1 glacial advance or limit of Pinedale Malta glaciation (limit of unit P1) Rocky Boy CONTINENTAL GLACIATION PI Williston [Line decorations on up-glacier side of limit] BEARPAW C Conrad Big Sandy Glasgow Culbertson BS

MOUNTAINS Brockton

M Late Wisconsin

Pendroy a

48˚ r 48˚

i EB a Poplar Misso s u Limit of glaciation (limit of unit LW)—Defined by Wolf Point ri R R ive stratigraphy and (or) surface morphology. Dashed where iv Frazer r er Lodge Pole Keene Lake S inferred Bynum Fort Peck C2 Limit of C2 regional glacial readvance in southwestern akakaw IL Alberta Eagleton CS Teton R iver LITTLE ROCKY MOUNTAINS ea Limit of regional glacial readvance (see fig. 1C) caused by Fort Peck Watford City Choteau Landusky Cartwright reorganization of glacial dispersal centers—Defined by Sun Prairie Lake stratigraphy and surface morphology. Dashed where Fort Benton inferred Iliad Sidney Limit of an ice-margin readvance or position of an ice- Power ver margin stillstand—Defined by stratigraphy and (or) surface Ri ri morphology. Dashed where inferred sou Mis LIMIT OF ICE-MARGIN READVANCE OR POSITION Limit of major glaciotectonic deposit or structure— Portage OF ICE-MARGIN STILLSTAND P1 Richey Defined by stratigraphy and (or) surface morphology SSC KILLDEER Illinoian MOUNTAINS SSC r Augusta Great Falls HIGHWOOD e Limit of glaciation (limit of unit IL)—Defined by stratigraphy MOUNTAINS and (or) surface morphology. Dashed where inferred; IL Grassy Butte Dunn Center dotted where buried by Pinedale 1 till wstone Riv Circle Golden Valley Limit of a major ice-margin readvance—Defined by surface er v Yel lo morphology iver BURIED LIMIT OF R LCB ouri Ri PRE-ILLINOIAN TILL Limit of an ice-margin readvance or position of an ice- Miss Denton Intake Judith Roy Jordan PW margin stillstand—Defined by surface morphology Valentine A

Cascade Pre-Wisconsin OT

AK Limit of till and glacial erratic boulders (unit PW)—Till is not present as far south as the limit of boulders

Mu Glendive 47˚ MONTANA 47˚ Pre-Illinoian (Pleistocene)

ss 114˚ NORTH D e

l s Southern limit of known surface exposure of till (unit PI) Lewistown h e l on north flank of Bearpaw Mountains lR Base modified and reprojected from 1:2,000,000 112˚ . Hebron Buried limit of till (unit PI), overlapped by Illinoian till National Atlas of the United States (Streams and Waterbodies, Dickinson 110˚ 106˚ (unit IL)—Mapped from distribution of exposures of till preliminary version, 2003; State Boundaries, 2002; and Cities and Towns, 2002) 108˚ Waterbodies and cities in Canada from 1:250,000 topographic maps Limit of glacial erratic boulders on eroded bedrock (unit from Natural Resources Canada (Lethbridge, 1995) and Department of Energy, SCALE 1:1 000 000 GB) Mines and Resources (Foremost, Cypress Lake, Wood Mountain, Willow WILLOW LETHBRID WOOD URN 25 0 25 50 75 100 MILES Stream or shoreline Bunch Lake and Weyburn quadrangles, 1967–1977) GE FOREMOST CYPRESSLAKE BUNCH WEYB MOUNTAIN LAKE Grid created for this map by the authors. r MBS 25 0255075 100 KILOMETERS Locality for stratigraphic section—See pamphlet for details. Transverse Mercator Projection Rive MRRS, Milk River Ridge; MBS, Mokowan Butte; TMRS, CUTBANK WILLISTON ri SHELBY HAVRE GLASGOW WOLF POINT u Datum NAD 1927 Spheroid CLARKE 1866 o Two Medicine Ridge; SMRS, St. Mary Ridge iss EB Location of erratic blocks from Canadian Shield LOCATION OF MAP AREA eM CHOTEA ORD CITY ttl U GREAT FALLS LEWISTOWN JORDAN GLENDIVE WATF LCB Li Lava Creek B volcanic ash site

INDEX TO 1˚ × 2˚ TOPOGRAPHIC QUADRANGLE MAPS DICKINSON USED IN PREPARATION OF THIS MAP SSC Sag or spillway—CS, Charbonneau Sag; CBS, Culbertson Sag; GS, Guardipee Lake Spillway; SSC, Shonkin Sag channels

Buried valley—BVMR, buried valley of ancestral Missouri River; 112˚ 110˚ 108˚ 106˚ 104˚ 102˚ 112˚ 110˚ 108˚ 106˚ 104˚ 102˚ 112˚ 110˚ 108˚ 106˚ 104˚ 102˚ BVMR BVYR, buried valley of ancestral Yellowstone River CANADA 51˚ 51˚ 51˚

49˚ N

UNITED STATES A BL

A

A A MP LW LW W

T CANADA CANADA E CANADA

RT

R RT

HEWAN

E

E Hall Coulee E

B

B

TCH

L

LB L LP A

A

A A ? K S 46˚ BL 50˚ 50˚ 50˚

SASKATCHEWAN SASKATC SA 102˚ EP PIEDMONT LB GLACIAL LOBE er Riv Babb Milk 104˚

ALBERTA EWAN ALBERTA ALBERTA WAN MP 49˚ SASKATCH 49˚ SASKATCHEWAN 49˚ SASKATCHE EB MONTANA MONTANA MONTANA MP IL 114˚ 112˚

OT DA NORTH

OT DAKOTANORTH 49˚ r IL e

MO OT DAKOTANORTH er MP v v MONTANA Ri LW Ri GLACIAL LAKE y ilk

NTANA M TWIN RIVER 48˚ 48˚ 48˚ ar

O ork M

SMRS ver ? NTAN hF KO t LW St. M HALL COULEE r No er iver GLACIAL LAKE KD TA SPILLWAY ANTELOPE LP R ST. MARY ilkRiv A erton Ri y M COULEE . t l r l iver kC e Babb ork Milk R SPILLWAY B F MRRS a n Wa le LB CutB Midd 47˚ A 47˚ B 47˚ C MP EP KD BL UNITED STATES UNITED STATES UNITED STATES er iv 0 50 100 150 200 MILES R Saint Mary lk MP Mi GLACIAL LAKE 0 100 200 KILOMETERS rk o CUTBANK EP F th u Browning P2 o GS 1 S k Figure 2. Schematic representation of regional ice-flow patterns during three Laurentide continental glacial CAL yr B.P.). During maximum late Wisconsin glaciation, the highest parts of the central and eastern active ice margins retreated rapidly in lowlands (Fullerton and others, 1995, 2000, in press). The positions ank Cree Cut B maxima. Note that the northern boundary of the map of glacial limits (above) is lat 50˚ N.; the northern blocks of the Cypress Hills and the Boundary Plateau were not glaciated. The predominant ice-dispersal of ice domes, ice divides, and ice saddles in Canada shifted (Shilts, 1980, 1982, 1985). The Keewatin Cut Bank TMRS TWO MEDICINE LOBE boundary in this figure (1A–C) is north of lat 50˚ N. The west boundary of the map of glacial limits is west of center was either (1) a Patrician center south or southwest of Hudson Bay in Canada (Tyrrell, 1914; center subsequently became the predominant ice-dispersal center for Laurentide glaciation in southeastern eek nkCr ≈ tBa the boundary in this figure. A. Maximum Illinoian glaciation ( 140 ka). During maximum Illinoian Johnston, 1935) or a modeled dome in that general location (Clark and others, 1996, 1997), (2) a “Hudson Alberta, southern Saskatchewan, southwestern Manitoba, northeastern Montana, and northwestern North k k MP Cu LP or ee glaciation, regional ice flow in southwestern Saskatchewan was southward into Montana. Ice flowed dome” in the southwestern part of Hudson Bay (Dyke and others, 1982; Hughes, 1985, 1987), or (3) a Dakota. C. Regional readvance maximum (≈14,000 14C yr B.P. or ≈16,350 CAL yr1 B.P.) following F r North ank C Sprin Ethridge P3 P1 g C reek westward between the Sweetgrass Hills nunataks in Montana and the Cypress Hills (west block) nunatak in “Hudson ice divide” southwest of Hudson Bay (Dyke and Prest, 1987b). The flow was not from a distant collapse of a “northeastern” ice-dispersal center. A regional Keewatin-source glacial readvance in Alberta, Cut B Alberta and Saskatchewan. The central and eastern blocks of the Cypress Hills were glaciated. Westward dispersal center in Quebec or Labrador (Shilts, 1980, 1982, 1985; Veillette and others, 1999) or from an Saskatchewan, Manitoba, Montana, North Dakota, Minnesota, South Dakota, and Iowa culminated ≈14,000 East Glacier Park GLACIER NATIONAL PARK TWO MEDICINE ice flow in Alberta north and northeast of Glacier National Park was blocked by a large piedmont lobe of “ancestral Keewatin” ice divide (Dyke and Prest, 1987b). Ice from a second, subordinate Keewatin dispersal 14C yr B.P. (≈16,350 CAL yr B.P.) (Fullerton and others, 1995, 2000, in press). The regional ice flow LOBE

coalesced mountain valley-glacier ice in the valleys of the Oldman, Waterton, Belly, and St. Mary Rivers (see center west of Hudson Bay was forced far westward in Canada, and coalesced Keewatin ice and depicted similar to a reconstruction by Dyke and Prest (1987a,b); it is incompatible with a reconstruction of West Marias 14 Glacier Riv Figure 1. Expanded view of rectangular area near Glacier National Park. pamphlet). Ice from a second, subordinate dispersal center flowed southwestward, west-southwestward, and “Cordilleran” ice from the Rocky Mountains (Dyke and Prest, 1987a, b) flowed southeastward from central Laurentide ice sheet flow ≈14,000 C yr B.P. by Hughes (1987). Reconstructions of ice flow during d er wo Me icine East Glacier er T Ri icine Riv ver Geologic compilation and interpretation by David S. Fullerton westward through southwestern Manitoba (east of this map area), southeastern Saskatchewan, and Alberta into Montana. Southeastward regional flow of ice from central Alberta into Montana occurred only maximum late Wisconsin glaciation by Dyke and others (1982) and Andrews and Fulton (1987) depicted Park Two M ed northwestern North Dakota into Montana. The areal distributions and the clast lithologies of the subsurface during late Wisconsin glaciation. The regional ice flow pattern depicted in figure 1B is incompatible with regional flow at ≈14,000 14C yr B.P., not regional ice flow during maximum glaciation ≈20,000 14C yr B.P. and Roger B. Colton. Digital database by Charles A. Bush. deposits of the two documented pre-Illinoian Pleistocene continental glaciations in Montana (not mapped) reconstructions of Laurentide ice sheet flow during maximum late Wisconsin glaciation by Dyke and others (≈23,360 CAL yr B.P.). P2 Digital cartography and graphics by Charles A. Bush, k indicate that the regional pattern of ice flow during the maxima of both of those glaciations was similar to (1982), Fisher and others (1985), Andrews and Fulton (1987), Dyke and Prest (1987a,b), and Hughes ree LW Arthur W. Straub, and Diane E. Lane. Edited by Diane E. Lane ——— ger C 14 Bad that during Illinoian glaciation, and it was very different from the regional flow pattern during maximum late (1987). Later than ≈17,000 C yr B.P. (≈19,850 CAL yr B.P.), the “northeastern” dispersal center 1 14 14 14 230 238 Approved for publication June 23, 2004 The CAL ages are C ages calculated by calibration of the C time scale to sidereal years by comparison of C ages and Th/ U Marias Pass Valier Wisconsin glaciation (fig. 1B). B. Maximum late Wisconsin glaciation (≈20,000 14C yr B.P. or ≈23,360 collapsed and regional ice-flow patterns changed markedly. The ice thinned and stagnated on uplands, and ages of coral samples (see “Introduction” in accompanying pamphlet). Glacial Lake Cutbank

CON Any use of trade names is for descriptive purposes only T ek and does not imply endorsement by the U.S. Government INENTAL

Birch Cre Dupuyer For sale by U.S. Geological Survey Information Services, MAP SHOWING SPATIAL AND TEMPORAL RELATIONS OF MOUNTAIN AND CONTINENTAL GLACIATIONS ON THE NORTHERN PLAINS, Box 25286, Federal Center, Denver, CO 80225; 1-888-ASK-USGS A PDF file and GIS files for this map are available at PRIMARILY IN NORTHERN MONTANA AND NORTHWESTERN NORTH DAKOTA DIVIDE http://pubs.usgs.gov/sim/2004/2843/

Pendroy GLACIAL LAKE By CHOTEAU

48˚ 48˚ 114˚ David S. Fullerton, Roger B. Colton, Charles A. Bush, and Arthur W. Straub 112˚ Figure 3. Middle Pinedale and late Wisconsin Laurentide glacial limits in the Cut Bank 1˚ × 2˚ quadrangle. LW, late Wisconsin till; Printed on recycled paper 2004 MP, middle Pinedale till; P2, Pinedale 2 till. Line decorations on up-glacier side of limit.