Geologic Atlas of Brown County, Minnesota

Home , Central Minnesota, Little Cottonwood River

Prepared and Published with the Support of COUNTY ATLAS SERIES THE BROWN COUNTY BOARD OF COMMISSIONERS, ATLAS C-37, PART A MINNESOTA GEOLOGICAL SURVEY the Minnesota Environment and Natural Resources Trust Fund Brown County Harvey Thorleifson, Director REDWOOD Minnesota COUNTY as recommended by the Legislative-Citizen Commission on Minnesota Resources, Plate 3—Surficial Geology

255Qrk19 River AND the Minnesota Legacy Amendment's Clean Water Fund

255 T. 112 N. Qf R. 33 W. Qa

- Ql

- 31

- 270

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- - RENVILLE

- Qhl 34

- COUNTY -

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- 300 NICOLLET 94° 45' W. Qc COUNTY 6 Qth Qrk Qhl 1 6

Lone Tree SURFICIAL GEOLOGy Lake 300

Qhl Qf By A' A 300 EDEN Qpo T. 111 N. R. 32 W. Howard C. Hobbs and Alan R. Knaeble

300

Creek Qc

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- 2016

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240

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LOCATION DIAGRAM - )4 Qf Minnesota

Qpo

Qhl Qpo - -

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- 300 -- Qf River

- Ql R. 31 W.

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- 31

- 36 - 36 - 31 45° 22' 30" N. - 45° 22' 30" N.

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- - Qc 240

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Qhl Ql 1 6 Qpo - 94° 30' W. -

6 1 -

315 6 -

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Ql -

Qhl -

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Qhl - - CORRELATION OF MAP UNITS

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Evan - -

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B 315 - Wind Stream Ice Lake Slope Bedrock Ql -

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- 255 -

- Qsw deposits - deposits deposits deposits deposits

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- Qpo - Qth )68

315 285

Ql Ql - -

- Qpo Qth - 270 - Holocene

- - Qa Qf Qrk Qhl Qpo Qc

Ql - - - Qa

- MILFORD 300

T. 110 N. PRAIRIEVILLE HOME -

315 - -

- - Qsw Qt Ql

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315 - Qth QUATERNARY - 14 -

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- 240 - T. 110 N. Heiberg Member

- Qi Qth Qwh Pleistocene - - - Qhl - New Ulm Formation

315 -

Qpo -

- Qhl - New Ulm Qs

315 - -

- Qhl Dovray Member - -

- 270 -

315 - Qtd Qwd

- - - New Ulm Formation

- Sleepy 300 240 -

- - Eye -

Qhl -

- Lake 300

- - 315 - - 315

- CRETACEOUS - Ku -

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QcRiver 255

- Ql

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Qwh - Qc

- -

-- 300

- - 36 31 Qs Qpo Minnesota

315 - Cottonwood 31 - Cottonwood Qt 36 31 300 36 31 Qa

95° W. Sleepy Eye - 285 Qt 315 - Qt

R. 35 W. Cobden - River

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R. 34 W. - 34 MAP SYMBOLS

- 300 - Qt

- -

Sleepy 315 -

Qt - - Qwh Qwh Qth Ql - C' Geologic contact—Approximately located.

¤14 -

Qs 255 - Eye Creek

6 1 6

- 1 300 - 6 6 Qth 1

Qhl 315 1 6 15 Broad, irregular trough—Interpreted to be a buried subglacial drainage channel (tunnel valley) - 6 ) 315 1

- Qhl Qwh 300 Qt Qwh Qc River or a preexisting drainage valley that was subsequently partially filled by sediment. When

C - Qt Sleepy Qt Qsw - Qwh

- 315 300 - Qs NICOLLET COUNTY 315 Qpo Qc Qf the ice melted, an irregular line of lakes and depressions was left behind where buried ice Qs Qs Qth Qwh 315 Qwh Qpo 4 Qwh 300 blocks had previously existed. Ticks point downslope. 315 ) Bachelor Qpo Qf 330 Qth Boise Qa Clear 315 Eye Qwh Qth Lake Esker—A narrow, sinuous ridge of predominantly sand and gravel, interpreted to have been Coal 300 Qth 12 - Lake Qth Qt Qhl Lake Qf - - -

BLUE EARTH ------deposited by a meltwater stream in a tunnel under ice or in an ice-walled channel, primarily

Qa 300

Qs -

Creek Qwh - 68 COUNTY

45° 15' N. 300 Qwh - ) identified by lidar imagery. Consists of fluvial sediment commonly covered by a cap of till.

Qwh -

300 -

Ku 315 - 45° 15' N. School -

Qth - Cottonwood In many places the feature is difficult to differentiate from crevasse ridges. Arrowheads

315 - -

Qs - - - - 270 Mine Zanders Qth Lake Qth -

Qa 315

- D' Qwh - Springfield 258 315 Qs River Lake Qc point in the inferred direction of meltwater flow and sediment transport. Qt ) - Qt Little River T. 109 N. Qs Qth 315 General flow direction of a meltwater stream—The arrow points in the direction that glacial 330 Qth 285 ¤14

N COTTONWOOD - meltwater last flowed within the unit. Where shown in units and (washed till), ORTH STAR Qwh Qs LEAVENWORT - Qwh Qwd

D BURNSTOWN H STARK SIGEL - Qt Creek 300

Qtd Qth Qs Qt -

Qhl Qpo Qwh Qs - there may be thin sand and gravel deposits over the washed till. -

- Qhl

Qwh- Qs 315 -

Qwh River

Qs - T. 109 N. Ice margin—Highly generalized inferred location of an ice margin based on topographic evidence -

Qt -

- -

300 - Ku Cottonwood Qa Qwh Qwh - and on the pattern of glacial meltwater flow. The presence of ice is required to explain why

Qwh Qth - Qtd 315 Juni Ql water was diverted from flowing down the regional slope; inasmuch as the flow pattern was Qwd 315 330 Gilman Qth Lake Qwh extremely complex, these lines should be seen as representative of a sequence of unmapped Lake Qwh

Qth - Qth

Qs Qi ice margins (Fig. 5).

Cottonwood -

------

- - Qwh - 315

315 -

- Qth 315 - Qth

330 - Ice-walled lake plain—Interpreted to be the approximate extent of sediment deposited in ice-walled -

River - Qs

- Qth Qth -

- -

Qpo - Qs Qs -

- Qs 36 31 36 31 31 36 Little lakes that formed on or in ice before the ice melted. Mapped in one place (T. 110 N., R. 31

- 330 Qhl 36 31

Qtd - 36 31 36

31 330 - Qwh

REDWOOD COUNTY - Altermatt Qwh W., secs. 27, 28, 33, 34) where slightly higher relief is vaguely visible on lidar imagery.

- Qwd Cottonwood Qs - Lake Qwh 315 M 330 Qhl Crevasse ridge—Primarily sand and gravel deposited by meltwater in a crevasse in glacial ice.

o 330 Qhl

u Qtd -

Q- td

nd Qth 300 - -

330 330 - When the surrounding ice melted, sediments remained, forming a straight or slightly sinuous

- Qa -

6 -

- 1 6 1 6 - 1 6 Qs 1

1 6 1 6 - ridge above the adjacent landscape. Deposits may contain lake sediment and in places till

COUNTY Ql - Qth

330 330 330 - Creek Qs Qwh - may cap or be interlayered with sand and gravel. Ridges are commonly transverse to the Qpo 330 315 Qwh

- - Qwd - E' - -

Qpo - inferred ice-flow direction, concave up-ice, and visible on lidar imagery. 330 Qs - COTTONWOOD -

- 315 -

315 - Precambrian bedrock, undivided—Granite, gneiss, and quartzite (see Plate 2, Bedrock Geology) . Qa Qs Qpo -

258 River -

E ) Qhl These bedrock types are present throughout the entire county beneath either Cretaceous

Qs Cottonwood - -

330 -

Little - and Paleozoic bedrock or glacial deposits. They are exposed at the surface in only a few -

- Qpo Qtd 315 Ql places, the most notable of which is in the Minnesota River valley at the northern tip of the

- Qth Qa Qs - county.

- - 300

- Qpo

- - -

Qwd Qwd - Qwd - -

T. 108 N. Qs Qth - Qpo Ql

- -

- 315

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------Qpo

- LA LINDEN M L - KE H STATELY U LIGAN - ALB ANSKA T. 108 N. BASHA - IN Hanska

W Qwd - Qhl -

Creek Qth -

River - Omsrud

- - -

- - Lake -

- - - - 315

- Linden

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- - Lake

- - F' -

330 - -

Qtd ------

- 257

Qtd - ) RENVILLE

Qs - - Lake

- 315

Mound - -

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- 3

- Hanska

345 4 -

) - Qh- l -

345 - Qth

Cottonwood -

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F' - Qwd -

45° 7' 30" N. - -

- 45° 7' 30" N. -

- - 315

- - - REDWOOD

Qtd -

345 Qtd - 1 - )15

Little - Qpo - - 315 Qhl

31 Qtd - Qhl Elevation (feet above mean sea level)

360 Qwd 31 36 31 36 31 36 Qs 31- 36 31 NICOLLET

36 - 36 High: 1,995 0 40 miles

- - - 375 - - Qth Qpo BROWN 4 Comfrey Wood Qpo Qi Ql Lake Ql Ql 0 60 kilometers R. 35 W. R. 32 W. R. 31 W. R. 34 W. COTTONWOOD COUNTY WATONWAN COUNTY R. 33 W. R. 30 W. WATONWAN COUNTY Low: 682 95° W. 94° 45' W. 94° 30' W. BLUE EARTH GIS compilation by R.S. Lively 5 Glacial River Warren channel Digital base modified from the Minnesota Department of Edited by Lori Robinson Transportation BaseMap data; digital base annotation by SCALE 1:100 000 COUNTY BLUE EARTH the Minnesota Geological Survey. Villard 1 0 1 2 3 4 5 MILES Member Elevation contours were derived from the U.S. Geological Survey LAKE PEPIN WATERSHED 2 30-meter Digital Elevation Model (DEM) by the Minnesota 1 0 1 2 3 4 5 6 7 8 KILOMETERS SHEAR ZONE Geological Survey. Universal Transverse Mercator Projection, grid zone 15 contour interval 15 METERS Heiberg 1983 North American Datum Member INDEX TO PREVIOUS MAPPING Minnesota River

INTRODUCTION now the town of Leavenworth, the meltwater flow left the line of the present day Cottonwood River Qt Terrace deposits—sand and gravel—Thin overbank fine-grained sand and silt overlying of the county (Plate 4, cross sections). In a number of places in west-central and BROWN COUNTY and flowed southeast across the course of the Little Cottonwood River and into the Lake Hanska channel sand and gravel. Deposits are commonly thin (less than 10 feet [3 meters] southwest Brown County, Dovray Member sediments may be interbedded with or This map portrays the primary sediment, its distribution, and its origin in the upper several meters channel (see broad, irregular trough in Map Symbols). thick) over till. The sand and gravel is outwash that may have been derived from overlie Heiberg Member till. This inverted or mixed stratigraphy is interpreted to Table 1. Physical characteristics of glacial deposits in the Brown County region (includes both surface and subsurface beneath the topsoil. Soils form in the uppermost geologic materials; thus a soil map provides clues deposits; see Plate 4, Quaternary Stratigraphy). When the ice margin retreated to the position shown in Figure 5D, a new channel formed parallel glacial meltwater of more than one ice lobe. The terrace is above the modern suggest that active Heiberg Member ice was incorporating Dovray Member stagnant to the material below in which it formed. The soil mapping units of Brown County (Christensen Glacial Lake to the ice margin, cutting a valley now occupied by Sleepy Eye Creek. A large flow continued floodplain because stream erosion later incised deeper into the valley. Mapped in ice and sediment. Minnesota and others, 1988; Natural Resources Conservation Service, 2014) were classified and color-coded the lower reaches of the Cottonwood and Little Cottonwood Rivers. SOURCE AREA NORTHWEST NORTH–NORTHWEST NORTH–NORTHEAST NORTHEAST along the line of the Cottonwood River in a now-abandoned channel approximately located near Qtd Till—unsorted sediment—Diamicton with similar characteristics to that of the Heiberg into surficial map units based on texture and inferred geologic origin, and digitally overlain on PROVENANCE RIDING MOUNTAIN WINNIPEG RAINY SUPERIOR the town of Iberia, where it was diverted east along the ice margin. West of the town of Searles, Member, but generally having a more sandy loam texture with less shale (Plate 4, the topography. Interpretation of topography was based on a 1-meter lidar hillshade image and HOLOCENE and Pleistocene the channel split; a northern fork flowed along the line of the Little Cottonwood River, and another Table 1). LOBE Des Moines Pre-Wisconsinan Wadena Pre-Wisconsinan red on 1:24,000-scale topographic map quadrangles. Geologic contacts were drawn on this base and Glacial River Warren sediment—sand and gravel—Sand and gravel, poorly to well- fork flowed south of Searles. Both flowed into Blue Earth County and eventually emptied into the Qsw Washed till—unsorted sediment—Similar lithologic characteristics to unit but TILL TEXTURE Sandy loam, loam, Sandy loam, silt loam, Sandy loam Sandy loam checked against well logs included in the Minnesota Geological Survey County Well Index. sorted and bedded. Deposits compose the terraces above the modern floodplain of Qwd Qtd Minnesota River. washed by glacial meltwater; similar in processes to unit . Located in the and clay loam and clay loam Field work that included descriptions of exposures and sampling of sediment also provided data the Minnesota River, but are also shown on the cross sections (Plate 4, Quaternary Qwh Figure 5E shows the Heiberg Member ice margin north of the Cottonwood River for the first southwest portion of the county along drainage channels in the eroded landscape TILL COLOR Figure 1. Digital Elevation model (U.S. Geological Survey, 2008) of the middle Minnesota River used in the compilation of this map. The principal author (Hobbs) collected samples in 2012 from Stratigraphy) extending beneath the terraces and modern alluvium, backfilling the time, and meltwater flow followed the entire length of the Cottonwood River to the Minnesota northeast of the base of the Prairie Coteau. Oxidized Light olive-brown Light olive-brown Yellow-brown Brown to red-brown watershed in south-central Minnesota showing topography in the vicinity of Brown County (modified road and stream cuts, gravel pits, basement excavations, and 63 soil borings drilled to depths ranging channel that was eroded (in some places to bedrock) by glacial River Warren during River. Unoxidized Gray to dark gray Gray to dark gray Gray to brown-gray Gray to red-gray from Jennings and others, 2011). Black labeled arrows denote the ice-flow path of two separate from 5 to 24 feet (1.5 to 7.3 meters). Additional samples included surficial materials collected by catastrophic discharge from glacial Lake Agassiz. The city of New Ulm was built CRETACEOUS but confluent ice streams that are interpreted to have deposited the Heiberg and Villard Members Jennings (2010) from sites scattered across the county as part of an earlier project (see Index to As Des Moines-lobe ice retreated, stagnated, and melted, a complex network of ridges and on a glacial River Warren terrace, which is considered a strath terrace where the PEBBLE TYPE Cretaceous bedrock—Interbedded sandstone, siltstone, and claystone (see Plate 2, of the New Ulm Formation, and dashed lines indicate what is inferred to have been a shear zone Previous Mapping). The secondary author (Knaeble) described and sampled approximately 150 irregular terrain was revealed. The interpreted crevasse ridges show the approximate ice-flow sand and gravel is thin on the lower part of the terrace. Here the unconsolidated Ku Carbonate Common Common to abundant Uncommon to common Uncommon to common Bedrock Geology). Unit generally consists of small areas exposed by erosion in the ice at their confluent boundary. Only sediment from the Heiberg Member was deposited in exposures along the Minnesota River bluffs in 2009 (Jennings and others, 2012; Meyer and others, direction because they are subtly concave up-ice in west-central Brown County. As ice retreated pre-Wisconsinan glacial deposits and Cretaceous bedrock have not been completely Gray-green rock Uncommon to common Uncommon to common Uncommon to common Common along the bottom and side walls of river valleys where not covered by colluvium, Brown County. A blue labelled arrow also shows the flow direction of the much younger glacial 2012a, b; Jennings and Adams, 2013) and 2010 (Knaeble, 2013), the Little Cottonwood River (in to the northeast, the flow direction became more southerly, reflected in the east–west orientation eroded and may be present beneath thin sand and gravel. Red felsite Absent to rare Absent to uncommon Rare to uncommon Uncommon to common outwash, and alluvium. In areas near and surrounding these outcrops, this unit may 2013), and the Cottonwood River (by canoe in 2013; see Index to Previous Mapping). Knaeble of the crevasse ridges in the central part of the county. The northern part of the county, the center Gray shale Uncommon to abundant Absent to common Absent Absent River Warren in its channel. Pleistocene be shallowly buried by material of the adjacent units. Rectangular delineations additionally collected samples from eight rotary-sonic borings drilled to bedrock in 2013. These of the Des Moines-lobe trough, is dominated by lake basins. Meltwater ponded in low areas of southwest of Springfield are Cretaceous clay pits. Further to the southwest near the data are also used for mapping subsurface deposits (Plate 4, Quaternary Stratigraphy). the flat landscape, and in a few places, small lakes were held in by ice (ice-walled lake plains). A Late Wisconsinan thin layer of sediment composed primarily of clay and silt (unit Ql) from the stagnant meltwater Cottonwood River, in areas too small to be mapped, blocks of Cretaceous bedrock GLACIAL HISTORY was deposited in both of these areas. Many of these lakes and shallow wetlands persisted into Peoria Formation appear to have been excavated by glacial ice and later deposited with the glacial sediment. At one site in a gravel pit too small to be mapped, about 0.5 mile (0.8 postglacial times (unit Qhl). Eolian silt and sand—Unbedded, silty, fine- to medium-grained sand with a few Maskwa ice stream Numerous glaciers traversed what is now Brown County during Pleistocene glaciations that Eventually Des Moines-lobe ice retreated out of Brown County to the northwest and into the granules. Unit is olive-brown (2.5Y 4/4) in color. Both sand and silt are calcareous, kilometer) south of the Cottonwood River (T. 109 N., R. 35 W., sec. 35, southwest 54° began about 2.6 million years ago (Plate 4, Quaternary Stratigraphy). Most near-surface sediments Red River Valley, where it is called the Red River lobe (Johnson and others, 2016). Here the natural with a leached zone at the surface. Interpreted to be windblown sand deposited corner), some Cretaceous bedding was tilted 45°. in Brown County were deposited during the Late Wisconsinan, the most recent glaciation, which slope of land is to the north, and water accumulated between the ice front and higher land to the during the last glaciation derived from nearby meltwater channels associated with Carbonate peaked about 20,000 years ago and largely ended by 10,000 years ago. During this glaciation south, creating the early stage of glacial Lake Agassiz. Meltwater from the retreating ice margin unit Qs. This thin (less than 2 feet [0.6 meter]) unit is mostly mapped on the basis REFERENCES rocks the county was covered several times by ice of the Des Moines lobe, a southern extension of the as far away as Alberta funneled into the lake, and it eventually overflowed south. Vast amounts of of well-sorted sand soils adjacent to, but not in, meltwater channels. In some places, Numbers in parentheses correspond with those shown on the Index to Previous Mapping 53° Shale & Laurentide Ice Sheet, which deposited sediment as the ice sheet advanced and retreated. Des Manitoba Escarpment carbonate water drained southeastward from glacial Lake Agassiz to create the glacial River Warren valley, these sands may be meltwater deposits from a period before the channel was fully Christensen, K.A., Domeier, M.J., and Anderson, R.W., 1988, Soil survey of Brown County: U.S. Moines-lobe ice advanced southeastward along a broad trough centered over the modern day trench rocks now occupied by the underfit Minnesota River. The glacial River Warren valley is incised into the cut. Shown by a pattern overlain on other units. Department of Agriculture Soil Conservation Service, 181 p., 37 pls., scale 1:20,000. Winnipeg containing the Minnesota River (Fig. 1). The southwest flank of the lobe was partly constrained glacial sediment to a depth of approximately 200 feet (61 meters) and locally exposes underlying New Ulm Formation—Includes sorted and unsorted sediments deposited by the Des (1) Gowan, A.S., and Jennings, C.J., 2016, Surficial geology, pl. 3 of Setterholm, D.R., project SASKATCHEWAN by a bedrock high composed of Sioux Quartzite (Plate 2, Bedrock Geology), although ice covered SASKATCHEWAN 52° pre-Wisconsinan glacial deposits and bedrock (map units Ku, Pu) along the northeastern boundary Moines lobe. Diamicton (till) of the New Ulm Formation is unsorted, unbedded manager, Geologic atlas of Redwood County Minnesota: Minnesota Geological Survey County MANITOBA MANITOBA the quartzite in southwest Brown County and left behind thin glacial deposits. Southwest of this NORTH DAKOTA of the county adjacent to Renville County (Jennings and Adams, 2013). The waters of glacial sediment with a sandy loam to loam texture, which contains clasts of gravel, scattered ONTARIO bedrock high previous glaciations had piled up many thick deposits in the area forming a highland, Atlas C-36, 5 pls., scale 1:100,000. River Warren eroded much of the saprolite that covered the deeply weathered crystalline bedrock, cobbles, and rare boulders. Materials deposited directly by ice and not altered are trending northwest, called the Prairie Coteau. The northeast-facing slope of the Prairie Coteau is Hobbs, H.C., 1998, Use of 1-2 millimeter sand-grain composition in Minnesota Quaternary studies, resulting in the irregular, knobby shape of the exposed bedrock and scattered rounded corestones referred to as till. Ice retreat or stagnation may be followed by another advance Grand Forks straight and uniform for a long distance, and appears to have been subjected to erosion by the Des in Patterson, C.J., and Wright, H.E., Jr., eds., Contributions to Quaternary studies in Minnesota: Riding 51° (Patterson and Boerboom, 1999). The rapid incision created multiple terrace levels in the glacial from a slightly different source area that may lay down a till of slightly different Gray shale Moines lobe as it widened the trough in which it flowed. Minnesota Geological Survey Report of Investigations 49, p. 193-208. Mountain River Warren spillway. The city of New Ulm is built on the widest terrace composed of glacial River composition. Individual layers with a more or less distinct composition and defined Missouri Coteau Sandstone The Des Moines lobe carried a distinctive mix of sediment derived in large part from Manitoba, (2) Jennings, C.J., 2010, Sediment source apportionment to the Lake Pepin TMDL—Source 95° 94° Warren sediment (unit Qsw). Lower parts of the terrace may be a strath terrace locally because it areal extent within the New Ulm Formation have been formally described and are Bismarck Fargo DES Saskatchewan, and eastern North Dakota (Fig. 2), where the bedrock contains significant amounts of characterization Middle Minnesota watershed: Minnesota Geological Survey Open-File Report Crystalline rocks may have only thin sand and gravel over Cretaceous bedrock (unit Ku) and older Pre-Wisconsinan therefore referred to as "members" (Johnson and others, 2016). A typical New Ulm Grantsburg 10-1, scale 1:100,000. Pembina Escarpment gray Cretaceous shale (Fig. 3). The mixture of sediment and rock types from this regional source till deposits. The incision caused the tributaries (located mostly in former meltwater channels) Formation member has a loam matrix texture, is yellow-brown where oxidized, and Buffalo sublobe area is categorized in Table 1 and exemplifies what is called the Riding Mountain provenance, (3) Jennings, C.J., and Adams, R.S., 2013, Surficial geology, pl. 3 of Setterholm, D.R., project corridor MOINES to down-cut as they adjusted their gradients to the new local base level, a process that continues dark gray where the matrix is unoxidized; mottled colors record seasonal saturation. MINNESOTA WISCONSIN named after Riding Mountain on the Manitoba Escarpment. Unsorted glacial sediment (till) of the today (Jennings and others, 2012). The Cottonwood and Little Cottonwood Rivers have fairly steep The matrix is calcareous; that is, it contains calcium carbonate, which effervesces in manager, Geologic atlas of Renville County, Minnesota: Minnesota Geological Survey County SOUTH DAKOTA ° Des Moines lobe consists of approximately equal portions of sand, silt, and clay, along with lesser Atlas C-28, 5 pls., scale 1:100,000. 93 Bemis moraine gradients in their lower reaches, where their floodplains are flanked with alluvial terraces, former weak hydrochloric acid, except where the upper few feet are leached of carbonate by Moland 92° ° MONTANA 91 ° Bemis amounts of pebbles, cobbles, and boulders. Ice from this general direction crossed Minnesota floodplains that have been left behind by deepening of the channels. The upper reaches of both water percolating through the soil. Coarser-grained particles ranging from granules (4) Jennings, C.J., Lusardi, B.A., and Gowan, A.S., 2011, Surficial geology, pl. 3 of Meyer, G.N., 90 Minneapolis Sandstone multiple times, leaving a complex record of similar-looking glacial materials having slightly different 48° Verdi streams lack terraces, and the floodplains are only slightly lower than the surface of the outwash to boulders include Precambrian igneous and metamorphic rocks, limestone and project manager, Geologic atlas of Nicollet County Minnesota: Minnesota Geological Survey BROWN ages and compositions. Collectively these are called the New Ulm Formation (Johnson and others, deposited when the valley was originally formed. Smaller streams eroded gullies into the sides of dolomite of Paleozoic age, and Cretaceous clasts, mainly of gray Pierre Shale. The County Atlas C-25, 6 pls., scale 1:100,000. 0 60 mi NORTH DAKOTA COUNTY 2016). Each layer (member) within the New Ulm Formation is interpreted to represent a separate the glacial River Warren channel and built alluvial fans (unit ) at the base of the steep slopes, standard size fraction for classifying and counting rock types is the 1-2 millimeter 0 80km Qf (5) ———2012, Surficial geology, pl. 3 of Meyer, G.N., project manager, Geologic atlas of Blue BROWN Carbonate IOWA ice advance of the Des Moines lobe (Lusardi and others, 2011). On the Surficial Geology map two 108° 107° 106° 105° 104° 103° 102° where the water slowed and was unable to carry its sediment load. In some places, streams have 47° very coarse-grained sand fraction (Hobbs, 1998). Lithologic characteristics vary Earth County, Minnesota: Minnesota Geological Survey County Atlas C-26, 6 pls., scale 47° Alexandria moriane COUNTY rocks (buried) members, the Heiberg and the Dovray, are recognized in Brown County. Two older members, the 0 60mi cut small channels into their fans. Colluvium (unit ) has covered the steep slopes with a mixture Figure 2. Pattern of ice flow from the northwest LOBE Qc somewhat from one till sheet to another (Lusardi and others, 2011), which allows 1:100,000. 0 80 km IOWA Ivanhoe and Moland, are present beneath the surficial units as depicted on Plate 4. Pre-Wisconsinan MINNESOTA Bemis of the deposits that make up the slope, both along the edge of the Minnesota River valley and on different members to be recognized and mapped (Plate 4, Table 1), but they also Johnson, M.D., Adams, R.S., Gowan, A.S., Harris, K.L., Hobbs, H.C., Jennings, C.E., Knaeble, that formed the Des Moines lobe; modified from complex Bemis glacial deposits are exposed at the surface in small areas (not large enough to be mapped) along the the sides of the tributary gullies. Soil, peat, and other organic deposits (for example unit ) have vary within each member, meaning that a single sample or set of samples may not Lusardi and others (2011). The flow pattern is Figure 3. Simplified bedrock subcrop of Minnesota and surrounding regions Qpo A.R., Lusardi, B.A., and Meyer, G.N., 2016, Quaternary lithostratigraphic units of Minnesota: 46° 46° valley walls of the Minnesota River and its tributaries, and are a major component of the subsurface superimposed on land-surface topography (Lusardi and others, 2011). The been forming on the land surface throughout postglacial time. be definitive. Minnesota Geological Survey Report of Investigations 68, 262 p. interpreted to have changed over time, which changed Prairie Coteau Des glacial stratigraphy. the composition of the till deposited, as represented 0 composition60mi of the glacial sediment in each of the Des Moines-lobe members Qs Outwash—sand and gravel deposited by glacial streams—Sand and gravel; ranging Knaeble, A.R., 2013, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., project manager, Geologic Moines The earliest advance of the Des Moines lobe is not well dated, but probably occurred before DESCRIPTION OF MAP UNITS by the various members of the New Ulm Formation 0 reflects80 km the various bedrock types their ice passed over, as well as eroded older from poorly- to well-sorted, commonly cross bedded to flat bedded. In places the ° atlas of Renville County, Minnesota: Minnesota Geological Survey County Atlas C-28, 5 pls., 45 the peak of the last glaciation, about 20,000 years before present. Deposits from this advance are (Lusardi and others, 2011). 45° glacial sediment and saprolith (weathered bedrock). QUATERNARY unit is capped by finer-grained sediment, either windblown sediment or a weathered scale 1:100,000. exposed in places along the Minnesota River valley from Brown County eastward on the slopes layer, usually thin and restricted to the soil profile. Deposited by glacial meltwater Lusardi, B.A., Jennings, C.E., and Harris, K.L., 2011, Provenance of Des Moines lobe till records Figure 4. Outline of the Des Moines lobe, showing the Bemis of the river channel and its tributaries, as well as on the east side of the lobe beyond the younger Holocene streams. Undivided as to member and may contain sediments from more than one ice stream catchment evolution during Laurentide deglaciation: Boreas, v. 40, p. 585-597. 44° moraine, as well as deposits of the earliest ice advance (shaded), deposits of the Bemis moraine (Fig. 4), and have been named the Moland Member (subsurface units member. 44° SOUTH DAKOTA Qpo Peat, organic material, and muck—Wetlands and drained wetlands containing partially Doi: 10.1111/j.1502-3885.2011.00208.x. BROWN COUNTY the Moland Member in the southeast, and the Verdi Member Qsm and Qtm on Plate 4). The Verdi Member (Johnson and others, 2016) may be the correlative decomposed organic matter (peat) and fully decomposed organic material with a Ql Glacial lake sediment—silt and clay—Gray silty clay and clayey silt; calcareous and in the southwest. unit on the west side of the lobe. Both members contain less shale than subsequent deposits of Meyer, G.N., Knaeble, A.R., Lusardi, B.A., Jennings, C.E., and Gowan, A.S., 2012a, Quaternary IOWA mixture of silt and clay (muck). These deposits formed in depressions—both swamps unbedded. Interpreted to have been deposited in small glacial lakes that commonly are the Des Moines lobe. stratigraphy, pl. 4 of Meyer, G.N., project manager, Geologic atlas of Blue Earth County, associated with depressions. Most of these lakes have been drained for agriculture, and shallow lakes. The irregular topography of glaciated landscapes, especially Minnesota: Minnesota Geological Survey County Atlas C-26, 6 pls., scale 1:100,000. After a period of glacial retreat, the Des Moines lobe advanced again and deposited the Ivanhoe areas where ice stagnated, created many isolated depressions. Although the surface and probably are capped by post-glacial lake clay. Includes an ice-walled lake where Meyer, G.N., Lusardi, B.A., Knaeble, A.R., Jennings, C.E., and Gowan, A.S., 2012b, Quaternary Member (units Qsi and Qti on Plate 4). When ice was at its maximum extent, its deposits formed sediment in this unit is highly organic, deeper layers in some depressions are chiefly the sediment may be bedded and include some fine-grained sand. the Bemis moraine (Fig. 4). Ivanhoe Member deposits are the surface unit on the Prairie Coteau stratigraphy, pl. 4 of Meyer, G.N., project manager, Geologic atlas of Nicollet County, Minnesota: inorganic silt and clay. The distribution of these materials was modified from the Ice-contact stratified sediment—sand and gravel—Sand and gravel, locally silty and just southwest of Brown County, but are present only in the subsurface in this county. Qi Minnesota Geological Survey County Atlas C-25, 6 pls., scale 1:100,000. A. B. C. Natural Resources Conservation Service (2014). This unit is similar to units Qp poorly to moderately sorted; cobbly in places. Bedding ranges from well-developed The ice that deposited the Bemis moraine stagnated, but had not completely melted when another Minnesota Department of Natural Resources, 2010, Lidar elevation, Minnesota elevation mapping and Qo in adjacent Renville and Redwood Counties, respectively. to vague and may be collapsed or faulted in places. May be overlain by till and pulse of ice arrived from the northwest, lapping onto the side of the Prairie Coteau, and depositing project: . Qa Alluvium—sand and gravel—Chiefly fine- to coarse-grained sand and fine- to coarse- includes lenses or layers of till. Deposited in close proximity to glacial ice. When the Dovray Member of the New Ulm Formation. The Dovray Member (units Qtd, Qwd) is at the grained gravel deposited in channels, with fine-grained sand and silt overbank the ice melted, sediment was left as ridges (eskers) or hummocky hills (collapsed Natural Resources Conservation Service, 2014, Web soil survey: U.S. Department of Agriculture, surface in the southwest corner of Brown County along the lower part of the Prairie Coteau slope. sediment on floodplains. The sediment in individual channels is too narrow to tunnel-valley fans). Most eskers are too narrow to map as a unit and are shown as line . A pattern of ridges along the Prairie Coteau slope are interpreted to be crevasse ridges (see Map map; however, channels have meandered and shifted over the years to cover nearly symbols. A tunnel-valley fan is mapped at the southeast end of Lake Hanska. Patterson, C.J., and Boerboom, T.J., 1999, The significance of pre-existing, deeply weathered Symbols), which typically form transverse to ice flow direction, and show that the ice was flowing the entire floodplain with channel sediment. Includes plant matter, generally large Heiberg Member—The uppermost member of the New Ulm Formation; distinguished crystalline rock in interpreting the effects of glaciation in the Minnesota River valley: Annals straight down the trough from northwest to southeast. woody debris in the channel layers, and finer-grained organic material in the overbank from other members by its high gray shale percentage in the 1-2 millimeter sand of Glaciology, v. 28, p. 53-58. After another period of stagnation, a renewed pulse of the Des Moines lobe deposited the sediment, which is interbedded in places with soil and peat. Low areas are locally fraction (Plate 4, Table 1; Johnson and others, 2016). In Brown County the average Ross, M., Campbell, J.E., Parent, M., and Adams, R.S., 2009, Palaeo-ice streams and the subglacial New Ulm New Ulm Heiberg Member ice New Ulm Heiberg Member of the New Ulm Formation over most of the county. The ice reached the base of landscape mosaic of the North American mid-continental prairies: Boreas, v. 38, p. 421-439. filled with thick silt to clay sediment, particularly oxbows in the Minnesota River gray shale percentage in till for 385 samples is 41 percent. Heiberg Member ice the Prairie Coteau slope in Brown County. This may have been one of the last major ice advances valley. Deposited by modern streams in channels and on floodplains. Qth Till—unsorted sediment—Primarily loam diamicton with scattered rocks and pebbles, U.S. Geological Survey, 2008, Shuttle radar topography mission: . Springfield 5, may represent minor readvances. In the west-central part of the county, the crevasse ridges Leavenworth deposits that are less than 10 feet (3 meters) thick over bedrock outcrop (Map 2.5Y 5/4 where oxidized to 2.5Y 4/1 where unoxidized. The surface expression formed by Heiberg Member ice show a more southerly ice flow trend than those of the Dovray Symbols). Bedrock may be present at the surface in a few places within this unit. is characterized by low-relief hummocks and hollows, low ridges, or an irregular Member ice. Present around bedrock outcrops in the Minnesota River valley. landscape. Unit is generally unsorted, but may include thin silty clayey sediment As ice deposited the Heiberg Member, a large meltwater flow system developed between the Qc Colluvium—mixed deposits—May have a variable composition depending on the material above the diamicton in low areas. The till may have greater sand content in some Prairie Coteau Prairie Coteau Prairie Coteau ice front to the northeast and the base of the Prairie Coteau slope to the southwest. Water initially exposed upslope. Deposits include a mixture of diamicton (till), soils, sand and crevasse ridges. flowed under the ice in the same direction as ice flow, as shown by a few parallel eskers and a possible gravel, pre-Wisconsinan sediments, saprolith, and local rock fragments near bedrock Washed till—unsorted sediment—Similar to unit , but may be overlain by a lag tunnel valley that may have scoured out what is now Wood Lake (mostly in adjacent Watonwan Qwh Qth outcrops. Deposited by gravitational slumping and soil creep on steep slopes. Unit of stones and/or thin patchy sand and gravel similar to unit . The distinction County to the south). As the ice at the margin melted, this drainage became a surface meltwater Qs is generally thin on upper slopes, thickening downslope. between washed till and outwash is considered to be where there is less than 5 feet channel flowing along the ice margin (Fig. 5A), eventually flowing into glacial Lake Minnesota Figure 5. Sequence of schematic ice margins as Heiberg Member ice (light gray) D. E. Fan deposits of alluvium—sand and gravel—Commonly bedded sand and gravel, but (1.5 meters) of sand and gravel over the till. Found along drainage channels, some to the southeast in Blue Earth County (Fig. 1). Spillway drainage from ice-marginal glacial lakes Qf retreated, with their associated meltwater channel (blue) flow directions (arrows). also includes layers of silt and silty clay loam. May contain interbeds of soil and of which may have also been used as spillways as glacial lakes drained, where further to the northwest may have contributed to the erosion of the channels. Thin eolian silt and Ice margins are generalized (they do not exactly match the ice margins on the variable amounts of disseminated organic debris. Forms fan-shaped deposits at surface expression is more subdued. Interpreted to have been washed by glacial fine-grained sand (pattern) is present, in places, on the uplands along the south side of some of surficial map), and only represent snapshots from a continually evolving ice sheet. the base of gullies as flow in the gullies slows and deposits sediment where small meltwater. Some meltwater channels are primarily filled with outwash, some are these channels. It most likely represents windblown (on the downwind side of the channel) material Meltwater flow paths are also generalized; not every channel is shown, nor are all streams enter the Minnesota River valley. Larger streams like the Cottonwood and primarily washed till, and some channels have "islands" of washed till surrounded Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is from the stream sediments deposited before the landscape was vegetated. intermediate phases. Some of the runoff is from locally melting ice, but much of Little Cottonwood Rivers do not have fans because their stream flow is capable of by outwash. based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may Heiberg Member ice then retreated (or retreated and readvanced) to the position shown in wish to verify critical information; sources include both the references listed here and information on file at the offices of the the meltwater was derived from further northwest. either relocating sediment along the river channel or carrying the sediment to the Dovray Member—Characterized by its sandy loam to loam till texture and by moderate Figure 5B. Meltwater flowed down the regional slope to the northeast for a few miles before being Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation conforms to A. Maximum extent of the ice that deposited the Heiberg Member; at this point Heiberg Member ice Minnesota River. amounts of gray shale in the 1-2 millimeter sand fraction (Plate 4, Table 1; Johnson sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously correct, however, Heiberg Member ice diverted to the southeast by the new ice margin. The meltwater channel followed the course of a meltwater flows southeast along the foot of the Prairie Coteau. Fine-grained modern lake sediment—Interlayered silt, clay, organic material, and sand and others, 2016). In Brown County the average gray shale percentage in till for and it should not be used to guide engineering-scale decisions without site-specific verification. New Ulm second former tunnel valley now occupied by Lake Hanska before flowing out of the county and Qhl B. Ice retreat 1 New Ulm deposited in post-glacial lakes; in some places includes drained ponds and lakes 98 samples is 21 percent. Forms the surface till in the southwest corner of the into glacial Lake Minnesota. Sleepy Eye county, but lies beneath the Heiberg Member till discontinuously throughout the rest C. Ice retreat 2 which are now being cultivated; may include some material mapped as unit Qpo. River Figure 5C shows the ice margin retreating in the west, allowing meltwater to erode a valley now D. Ice retreat 3; meltwater flow is along the Cottonwood River in western Brown Springfield Springfield Cottonwood Creek occupied by the Cottonwood River. In the east, the margin remained about the same. At what is Iberia Searles County, but along the Little Cottonwood River in eastern Brown County. Cottonwood E. Ice retreat 4; flow is established along the entire extent of the modern day River Little Cottonwood River. Cottonwood River Prairie Coteau Prairie Coteau

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