6. Minnesota River Valley Landslides
(Berthold, 2018) helped identify the geologic units Deep-seated slope failures that were likely involved in the landslides. Field work conducted in the summer and fall of 2018 along the Minnesota River focused on verifying these interpretations through the materials exposed in the slide area, as identified valley and tributaries by the shape of the scarp and deposit. Watershed districts in Hennepin County provided information Deep-seated, large slides are located on the locations of known erosion sites within their primarily along the Minnesota River watersheds. Spring horizons mapped by Minnesota valley and its tributaries. They are Department of Natural Resources geologist Dr. Greg Brick (MnDNR, 2017) were correlated with map units. entirely within the glacial sediment sequence. An understanding of the specific surfaces where failures occur, Geologic Background the location of springs, as well as Glacial deposits, including those of meltwater streams and lakes, cover all of Hennepin County. the history of valley formation helps The valley now occupied by the Minnesota River understand slide locations and future is the most recent, indirect feature of glaciation. occurrences. Although these are large, Glacial floodwaters emanated from the very large glacial Lake Agassiz and shaped the valley over a they are typically the slowest form of few thousand years. The creation of the valley now failure. Geotechnical investigations prior occupied by the Minnesota River was a destabilizing to development and wise land uses event for the entire basin. Adjustments to valley profiles and the creation of new tributaries are that protect the slopes from reactivation ongoing. Steps or knickpoints in the tributary-stream are prudent approaches. profiles record where adjustment is occurring, and they can be observed migrating upstream on human time scales. It is the continuous evolution of stream profiles that creates the freshest and most Methods susceptible slopes, but even the older steep slope Existing surficial geology maps of the Twin Cities areas can become active with changed hydrology, Metropolitan Areas (Hobbs et al., 1990; Patterson, vegetation or land use. 1992; Meyer and Patterson, 1999) and those updated during this project (Steenberg et al., 2018) provided pertinent regional geologic data that helped Glacial History understand the geologic setting of deep-seated The youngest glacial-age units in Hennepin County landslides. Water well logs, Minnesota Department are meltwater stream deposits found at the surface, of Transportation boring records, and Giddings-hole paralleling the modern Minnesota River but lying and rotary-sonic-core logs drilled for the Minnesota over 200 feet above the modern river valley. There, Geological Survey map project provided site- sand and gravel were deposited by meltwater specific information of units that were potentially streams as the ice retreated (units Qts, Qts1, Qts2 involved in landslide events. The depth to the on the cross sections shown in Figure 6.4). These failure surface estimated using hillslope expression deposits are over 100 feet thick in Eden Prairie on the mapped slides combined with kilometer- along Purgatory Creek. There are a few areas in spaced cross-sections through the surficial deposits
12 | Hennepin County Landslide Hazard Atlas Bloomington with thick deposits as well (Figures Formation of the Superior lobe was incorporated 6.1, 6.2, and 6.3). Because of the great thickness and (Johnson et al., 2016 and references therein). In some porosity of this unit, it is generally dry where it is places the till resembles sediment of the Des exposed next to the deep river valleys. However, Moines lobe before it crossed the St. Croix moraine, mapped as Villard (Qv) and Heiberg (Qh) members of the New Ulm Formation. Where it admixed more of the Superior lobe material, it is mapped as the Twin Cities Formation (Qt). Despite the color variation, the overall differences are subtle and based on minor changes in texture and lithologic composition. Prior to the Grantsburg sublobe advance, the Superior lobe advanced into the region from the northeast and deposited the reddish-brown till of the Cromwell Formation (Qc). Lake sediment composed of alternating layers of reddish clay and gray silt (Qcl) accumulated as Superior lobe ice Figure 6.1 — Terrace Sand and Gravel Deposits retreated. This lake is referred to Meltwater stream deposits along Purgatory Creek deposited as ice retreated as “Early glacial Lake Lind” and is a from the region. These sand and gravel layers are never saturated near significant unit in the subsurface deeply incised streams because of their thickness and permeability. (Berthold, 2018). These events are Photo by Mary Presnail. depicted in sequence (Figure 6.2). Even older glacial sediment from farther back from the bluff face it may be saturated. previous glaciations is found at depth, and thick One would therefore expect a steeply sloping water layers of glacial sediment and stream sediment have table surface that may intersect the bluff face at low accumulated in lows in the bedrock (Table 6.1). Dark elevation, or even in the bed of the Minnesota River, gray, clay loam to loam glacial sediment is exposed where groundwater would emerge as springs. in places in tributary valleys to the Minnesota River and has been identified as two members of the The next youngest event to affect Hennepin County Lake Henry Formation (Johnson et al., 2016 and was the advance of the Grantsburg sublobe that references therein; Berthold and Lively, 2018). emanated from the northwest, bringing loamy to clay-loamy glacial sediment that was deposited in hummocky, stagnant-ice terrain. This unit forms the surface of most of the county (Johnson et al., 2016 and references therein). As the Grantsburg sublobe entered the county from the west, it crossed older morainic topography of the underlying Superior lobe and proceeded to flow into the area recently occupied by it. The Grantsburg sublobe till is therefore highly variable and its classification depends on how much of the visibly different, red, sandy loam glacial sediment of the Cromwell
Minnesota River Valley Landslides | 13
of Red Dark 1 2
11 11 C (Clayton C (Clayton Light crystalline 14 88 86 12 70 2 18 87 12 74 18 8 72 19 9 grains counted Percentage of total C (Clayton and C (Clayton and Lusardi, B.A., of Lusardi, B.A., 14 Norvitch, R.F., of Norvitch, R.F., Sims, P.K., and and in Sims, P.K., Balaban, N.H., of Balaban, N.H., Patterson, C.J., C.J., in Patterson, C (Wright and Rubin, C (Wright and Rubin, C (Meyer, 1998). C (Meyer, 14 CLAST TYPE CLAST 14
Hennepin Hennepin County Sims, P.K., and Morey, and Morey, in Sims, P.K., Cretaceous C, and 15,000 Patterson, C.J., and Wright, Wright, C.J., and Patterson, 14
in Meyer, G.N., and Swanson, G.N., and Swanson, of Meyer, Paleozoic C and 12,030 Minnesota Geological Survey Minnesota Geological Survey ATLAS C-45, PART A A PART C-45, ATLAS 14
Tipping, R.G., project manager, R.G., project manager, Tipping, of Precambrian C and 12,030 C and 11,710
COUNTY ATLAS SERIES ATLAS COUNTY Plate 3—Surficial Geology 3—Surficial Plate C, 15,500 millimeter fraction counted of the 1-2 14 Patterson, C.J., and Wright, H.E., Jr., Wright, H.E., Jr., C.J., and in Patterson, 14 Bauer, E.J., project manager, Geologic Geologic E.J., project manager, Bauer, 14 Bauer, E.J., project manager, Geologic Geologic E.J., project manager, Bauer, of Percentage of total grains of Tipping, R.G., project manager, Geologic Geologic R.G., project manager, Tipping, of Setterholm, D.R., project manager, Geologic Geologic of Setterholm, D.R., project manager,
Setterholm, D.R., project manager, Geologic Geologic of Setterholm, D.R., project manager,
Minnesota Geological Survey Miscellaneous Miscellaneous Minnesota Geological Survey C (Meyer and Stefanova, 2009; Meyer, 2010). 2009; Meyer, and Stefanova, C (Meyer Setterholm, D.R., project manager, Geologic Geologic of Setterholm, D.R., project manager, Clay 14
REFERENCES Silt Minnesota Geological Survey Miscellaneous Map M-94, Miscellaneous Map M-94, Minnesota Geological Survey fraction Patterson, C.J., and Wright, H.E., Jr., eds., Contributions eds., Contributions Wright, H.E., Jr., C.J., and in Patterson, Surficial geologic map of the Shakopee quadrangle, Carver, quadrangle, Carver, geologic map of the Shakopee Surficial
Surficial geology of the New Brighton quadrangle, Minnesota: Brighton quadrangle, Minnesota: geology of the New Surficial Percentage of the Sand less than 2 millimeter
1997,
1966, weight) sample Surficial geologic map of the Watertown quadrangle, Carver, Hennepin, Hennepin, quadrangle, Carver, Watertown geologic map of the Surficial
MATRIX TEXTURE MATRIX total of (percentage Gravel Warren, W.P., and Croot, D.G., eds., Formation and deformation of glacial and deformation of glacial and Croot, D.G., eds., Formation W.P., Warren,
in
Age is in calendar years before present (cal YBP), calibrated using CALIB YBP), calibrated using CALIB Age is in calendar years before present (cal Age is in calendar years before present (cal YBP), recalibrated and averaged YBP), recalibrated and averaged Age is in calendar years before present (cal YBP), recalibrated and averaged Age is in calendar years before present (cal Age is in calendar years before present (cal YBP), recalibrated using CALIB YBP), recalibrated using CALIB Age is in calendar years before present (cal Ages are in calendar years before present (cal YBP), recalibrated and averaged YBP), recalibrated and averaged Ages are in calendar years before present (cal YBP), recalibrated and averaged Ages are in calendar years before present (cal
ey, p. 515-547. ey, samples of 1 2 3 4 5 6
7 49 34 17 56 25 19 Total number Total 73 7 54 20 30 1 16 23 52 76 25 15 9 73 13 14 116 381 4 41 39 20 40 26 34 G.B., eds., The geology of Minnesota: A centennial volume: Minnesota Geological Minnesota Geological A centennial volume: The geology of Minnesota: G.B., eds., Surv G.J., 1997, How glaciers entrain and transport basal sediment: Physical constraints: constraints: glaciers entrain and transport basal sediment: Physical G.J., 1997, How 16, p. 1017-1038. v. Quaternary Science Reviews, Hodder Education, 816 p. of in east-central Minnesota: Minneapolis, University compositional variability Minnesota, Ph.D. dissertation, 255 p. 1, p. 55-82. v. America: Quaternary Science Reviews, middle North Minnesota: Minnesota Geological Survey Wright County, Geologic atlas of A, 6 pls., scale 1:100,000. Atlas C-30, pt. County Balaban, N.H., and Hobbs, H.C., project managers, Geologic atlas of Dakota A, 9 Atlas C-6, pt. County Minnesota: Minnesota Geological Survey County, pls., scale 1:100,000. G.N., 2016, Quaternary lithostratigraphic A.R., Lusardi, B.A., and Meyer, Knaeble, RI- Investigations of Report Survey Minnesota Geological of Minnesota: units 68, 262 p. sublobe, and retreat of the Grantsburg recording the advance to Quaternary studies in Minnesota: eds., Contributions Wright, H.E., Jr., and RI-49, p. 49-60. Report of Investigations Minnesota Geological Survey deglaciation, Wisconsinan during the late to Quaternary studies in Minnesota: Minnesota Geological eds., Contributions RI-49, p. 7-14. Report of Investigations Survey Minnesota, the St. Croix moraine, Stearns County, Educational Series 7, 20 p. 124, p. 625-626. Science, v. Scott, and Hennepin Counties, Minnesota: Miscellaneous Map M-87, scale 1:24,000. Wright Counties, Minnesota: and Map M-108, scale 1:24,000. Atlas County Minnesota: Minnesota Geological Survey atlas of Scott County, A, 6 pls., scale 1:100,000. C-17, pt. H.E., Jr., eds., Contributions to Quaternary studies in Minnesota: Minnesota to Quaternary studies in Minnesota: Minnesota eds., Contributions H.E., Jr., RI-49, p. 15-26. Report of Investigations Geological Survey Atlas County Minnesota: Minnesota Geological Survey Wright County, atlas of C-30, 6 pls, scale 1:100,000. Counties, Minnesota: scale 1:24,000. project manager, Geologic atlas of Sherburne County, Minnesota: Minnesota Minnesota: Minnesota County, Geologic atlas of Sherburne project manager, A, 5 pls., scale 1:100,000. Atlas C-32, pt. County Geological Survey during Laurentide deglaciation: lobe till records ice stream catchment evolution 40, no. 4, p. 585-597. Boreas, v. atlas of Carver County, Minnesota: Minnesota Geological Survey County Atlas Atlas County Minnesota: Minnesota Geological Survey County, atlas of Carver A, 5 pls., scale 1:100,000. C-21, pt. Morey, G.B., eds., The geology of Minnesota: A centennial volume: Minnesota Minnesota A centennial volume: The geology of Minnesota: G.B., eds., Morey, p. 548-560. Geological Survey, northwest Wisconsin, Report of to Quaternary studies in Minnesota: Minnesota Geological Survey RI-49, 208 p. Investigations Miscellaneous Map M-178, scale 1:100,000. Minnesota Geological Survey Atlas County Minnesota: Minnesota Geological Survey atlas of Chisago County, A, 6 pls., scale 1:100,000. C-22, pt. atlas of Anoka County, Minnesota: Minnesota Geological Survey County Atlas Atlas County Minnesota: Minnesota Geological Survey Anoka County, atlas of A, 6 pls., scale 1:100,000. C-27, pt. project manager, Geologic atlas of Hennepin County, Minnesota: Minnesota Minnesota: Minnesota Geologic atlas of Hennepin County, project manager, A, 9 pls., scale 1:100,000. Atlas C-4, pt. County Geological Survey Abstracts with Programs, v. America Minnesota [abs.]: Geological Society of 41, no. 4, p. 5. 32, p. 24-35. central Minnesota: Quaternary Research, v. 25, no. 11, p. 987-990. v. Geology, during Heinrich events: reorganization and Walton, M.S., eds., Geologic and hydrologic aspects of tunneling in the Twin Twin aspects of tunneling in the M.S., eds., Geologic and hydrologic Walton, and Survey, Geological Minnesota Survey, Geological U.S. Minnesota: area, Cities Series, Map Miscellaneous Investigations Transportation and U.S. Department of I-1157, 7 pls., scale 1:24,000. Agriculture,
—Fine-grained sand to gravel of of —Fine-grained sand to gravel —Brown (7.5YR 4/4 to 10YR 5/3) (7.5YR 4/4 to 10YR 5/3) —Brown and By , and along the sides of and within , and along the sides of within 2018 Qvt Qti (Table 2). Surface expression of this of this expression 2). Surface (Table —Massive, reddish-brown (5YR 4/3) (5YR 4/3) reddish-brown —Massive, —Unsorted, olive-brown (2.5Y 4/4) 4/4) (2.5Y olive-brown —Unsorted, ; ice-walled stagnation plains are rare. stagnation plains are rare. ; ice-walled —Unsorted, reddish-brown (5YR 4/3) (5YR 4/3) —Unsorted, reddish-brown —Unsorted, light olive-brown (2.5Y 5/4) (2.5Y 5/4) —Unsorted, light olive-brown Qtt —Massive, olive-brown (2.5Y 4/3) where (2.5Y 4/3) where olive-brown —Massive, —Reddish-brown to brown loamy sand to loamy sand to to brown —Reddish-brown —Unsorted, olive-brown (2.5Y 4/4) where (2.5Y 4/4) where —Unsorted, olive-brown Qht Absent Common —Massive, light yellowish-brown (2.5Y 6/4) to (2.5Y 6/4) to light yellowish-brown —Massive, loamy sand loamy SUPERIOR Angela J. Berthold NORTHEAST Sandy loam to to loam Sandy The surface expression is generally less rolling is generally less rolling expression The surface Gray to red-gray to Gray Rare to uncommon to Rare Brown to red-brown to Brown Superior (Cromwell) Superior —The only sediments of the Cromwell Formation Common to common to Common Common to abundant to Common Qtt .
). Lacustrine sediment at this high elevation compared to the compared to the ). Lacustrine sediment at this high elevation but can also resemble unit but . The surface expression is primarily in the form of linear to is primarily in the form of linear to expression The surface . SURFICIAL GEOLOGY Qtt Qtt Qtt sandy gravel. The surface expression of this unit is limited because of this unit is limited because expression The surface sandy gravel. it but by later glacial events, and buried most deposits were reworked These deposits were generated at the mouths is typically hummocky. carrying where pressurized subglacial meltwater of tunnel valleys, coarse-grained sediment reached the edge of Superior lobe and subaerial deltas or alluvial fans. deposited the sediment as large-scale mined in the Maple Grove this unit has been extensively Consequently, marks the Another deposit in Prospect Park area for use as aggregate. unit was Where patterned, in the city of Minneapolis. highest elevation ice-contact deposits. Superior-lobe for use as aggregate. excavated differs lithologically because it contains greater than 5 percent red lithologically because it contains greater than 5 percent red differs is channelized in the west but expression The surface 2). clasts (Table numerous by marked is plain The east. the to plain broad a into expands ice blocks that depressions and pits representing former buried kettle Grantsburg- lakes. of these pits are now melted; many eventually and Villard, Cities, Twin Superior-lobe, eroded meltwater sublobe generating sand and Member deposits throughout its advance, Heiberg that contains both red felsite and shale in statistically significant gravel Cities Twin Therefore, this unit is described as part of the proportions. lithologic composition only and not its Member based on its mixed member. Ulm Formation New association with a specific Member outwash. underlying 10 to 15 feet (3 to 4.5 meters) of sandy loam to loamy sand underlying 10 to 15 feet (3 4.5 meters) of sandy loam loamy sand (unit more than unit stagnation as opposed to active-ice deposition. Fine-grained sand and and sand Fine-grained deposition. active-ice to opposed as stagnation Minnetonka basin along isthmuses and peninsulas silt within the Lake sediments in stagnant meltwater is the result of sorting finer-grained plain. Local sand lake ice blocks, such as an ice-walled between large Minnetonka indicate deltaic lenses along the edges of Lake and gravel into the basin. In all other mapped areas, meltwater flow meltwater Member till, washing deposited Heiberg previously locally reworked sediment. sediment and concentrating coarser-grained finer-grained away deposits. Member stagnation Heiberg This suggests deposition under active-ice conditions. Contains less conditions. Contains less This suggests deposition under active-ice than 5 percent red clasts, indicating only slight mixing with underlying Member till. deposits. Villard Superior-lobe (2.5Y 4/3) where oxidized, dark gray (2.5Y 4/1) where unoxidized. (2.5Y 4/3) where oxidized, dark gray 4/1) unoxidized. Unit is lithologically similar to unit light olive-brown (2.5Y 5/3) where oxidized, very dark gray (2.5Y 3/1) dark gray (2.5Y 3/1) (2.5Y 5/3) where oxidized, very light olive-brown small the of composition The loam. silt to clay silty unoxidized, where of mixed coarse-grained sand in this unit is indicative percentage of very similar to unit provenance, to very pale brown (10YR 7/4) where oxidized and finer-grained, silty silty (10YR 7/4) where oxidized and finer-grained, pale brown to very Lithologic composition is similar to clay to loamy sand and gravel. unit where oxidized, very dark gray (2.5Y 3/1) where unoxidized, diamict. dark gray (2.5Y 3/1) where unoxidized, diamict. where oxidized, very The uncommon. are boulders cobbles; and pebbles scattered Contains coarse-grained sand fraction lithologic composition of the very average 2. Generally contains less shale than unit Table in is shown concave up-ice moraines, but less linear and more rounded forms also less linear and more rounded forms also up-ice moraines, but concave The interpretation of these features to be push to a lesser extent. exist moraines is based on multiple soil borings the tops of silty clay loam, and silt loam (unit silty clay, encountering massive subsurface and was deposited during the stagnation of sediment-rich deposited during the stagnation of sediment-rich and was subsurface spots generated by the Superior ice in distinct low Grantsburg-sublobe this Where mapped at the surface, lobe and/or within bedrock valleys. ice in deposited during the stagnation of Grantsburg-sublobe unit was This stagnation method of the Superior lobe. a former tunnel valley from the more typical subglacial deposition of deposition is different interbedded with of diamict, generating a softer diamict complexly seams. silty clay and sand gravel deposits. stratigraphically occurs within the Heiberg stagnation sequence. Unit stagnation sequence. Unit stratigraphically occurs within the Heiberg sublobe of the Grantsburg probably represents a former ice-margin stagnation position east of Lake retreated to its final as it actively Member ice-contact deposits. Minnetonka. Heiberg and hummocky than unit and hummocky former meltwater channels in northeast Minneapolis. This unit was This unit was channels in northeast Minneapolis. former meltwater the slopes of push by sediment sliding down ways: generated in two between ice after soon deposit a gravity as lows in settling and moraines diamict. locally reworking the push moraines melted, and by meltwater Cities Member colluvium. Twin unit is highly variable. The unit was initially deposited in proglacial proglacial in deposited initially was unit The variable. highly is unit to the northeast. Continued sublobe advanced as the Grantsburg lakes the aforementioned push into led to deformation of the unit advance this unit can also be found undeformed, especially on moraines, but this unit underlies Additionally, sides of push moraines. the down-ice sediment boundaries. some modern lake beyond and extends Cities Member lacustrine deposits. surrounding topography implies ice-marginal deformation essentially deformation essentially implies ice-marginal surrounding topography land feature. Because proglacial sediments into a positive bulldozing the formation of these ridges is ice-contact in origin, it warrants deformed and interbedded Complexly unit. as a separate delineation and diamict were also inclusions of coarse-grained sand and gravel the faulted, road cuts pictured in Figure 4, which show found along two Where more rounded of these deposits. nature deformed, and complex with and mixes in shape, the unit is primarily loamy sand that overlies ice-contact deposits, such as near Minnetonka and the Superior-lobe Where Minneapolis. of neighborhoods Hill Lowry and Mawr Bryn to use as aggregate. excavated patterned, unit was ice-contact deposits. oxidized, very dark gray (2.5Y 3/1) where unoxidized, diamict. Contains oxidized, very lithologic Average scattered pebbles and cobbles; boulders are rare. Table in shown is fraction sand coarse-grained very the of composition The lithologic composition of this unit indicates much more shale 2. 41 percent) than units (average generally rolling and hummocky with numerous ice-walled stagnation stagnation with numerous ice-walled generally rolling and hummocky of ice stagnation. plains and ice-block melt-out depressions indicative and locally present is thin, patchy, Silt loam deposited in ponded water Member till. stagnation plains. Heiberg on the tops of ice-walled oxidized, dark gray (2.5Y 4/1) where unoxidized, loamy sand to gravelly oxidized, dark gray (2.5Y 4/1) where unoxidized, loamy sand to gravelly This unit is lithologically similar to both units sand. expression of this unit is limited to low elevation areas between push areas between push elevation of this unit is limited to low expression moraines associated with unit to brown (7.5YR 4/3 to 10YR 4/3) to olive-brown (2.5Y 4/3) where (2.5Y 4/3) where (7.5YR 4/3 to 10YR 4/3) olive-brown to brown where 3/1) to 2.5Y 3/1 to 10YR (7.5YR 3/1 dark gray oxidized, very pebbles and cobbles; boulders are unoxidized, diamict. Contains many common in places. Unit also includes lenses of sand, silt, and gravel coarse-grained very the of composition lithologic Average places. in 2. Table in sand fraction is shown When within this unit. compositional variability illustrate the complex it deformed and to the northeast, sublobe advanced the Grantsburg yellow diamict into its own red Superior-lobe incorporated existing distorted and blended, streaked, yellow and red generating diamict, diamict (Fig. 4). Red inclusions can also be found within red and yellow mixed diamict. Pervasively predominantly yellow can be found further to the till is uncommon in Hennepin County but sublobe continued to incorporate and northeast, where the Grantsburg Cities Member till. deposits. Twin Superior-lobe deform existing to brown (7.5YR 4/3 to 10YR 4/3) to olive-brown (2.5Y 4/3) where (2.5Y 4/3) where (7.5YR 4/3 to 10YR 4/3) olive-brown to brown dark gray (7.5YR 3/1 to 10YR 2.5Y 3/1) oxidized, very lithologic Average where unoxidized, silty clay loam to sandy loam. to similar is fraction sand coarse-grained very the compositionof unit mixed provenance. This unit is texturally similar to unit This unit is texturally provenance. mixed (10YR 4/4) where oxidized, dark gray (2.5Y to dark yellowish-brown loamy to loam clay silty loose unoxidized, where 4/1) 10YR to 4/1 for sand. Silt loam, and sandy loam are also possible textures this unit. Lithologic composition is similar to unit mapped at the surface in Hennepin County are ice-contact deposits. in Hennepin County are ice-contact deposits. mapped at the surface was but at the surface once abundant diamict was Cromwell Formation sublobe . by deposits associated with the Grantsburg later covered Common Common clay loam clay Loam to clay loam diamict Loamy sand to sandy gravel Loamy sand to gravelly sand Loamy sand to gravelly Loam to sandy loam diamict Silty clay loam to sandy Silt loam, sandy and loamy sand gravel Silty clay to loamy sand and gravel Silty clay to silt loam Loam to sandy loam diamict loam sandy to Loam Fine-grained sand to sandy gravel Silty clay loam to loamy sand NORTHWEST Absent to rare to Absent Sandy loam to to loam Sandy Light olive-brown Light Gray to dark gray dark to Gray
Cromwell Formation Cromwell MOUNTAIN RIDING Uncommon to common to Uncommon Uncommon to common to Uncommon Des Moines (New Ulm) (New Moines Des
Qti Qtl Qtt Qsi Qhi Qvt Qts Qtc Qst Qht Qsh
Physical characteristics of glacial deposits in Hennepin characteristics of glacial deposits in Hennepin Physical Oxidized Unoxidized Carbonate rock Gray-green Red felsite Red shale Gray quartz Clear but was able 1. T County. SOURCE AREA PROVENANCE TEXTURE TILL COLOR TILL PEBBLE TYPE LOBE (Formation) LOBE Qts Qts (Meyer, (Meyer, 6 Sand and gravel facies facies Sand and gravel ). Organic deposits and deposits and ). Organic . in composition but no no but composition in ) can be found at the land be found at the land ) can Ql Heiberg Member lacustrine Member lacustrine Heiberg Qp Qag
), forming what is now a series series a now is what forming ),
—Silty clay loam, silt loam, and —Silty clay loam, silt and Qsh WASHINGTON —Massive, yellowish-brown to gray, to gray, yellowish-brown —Massive, GOODHUE —Massive, fine-grained sand to gravel sand to gravel fine-grained —Massive, CHISAGO 2 —Sorted, massive, olive-brown (2.5Y 4/3) (2.5Y 4/3) olive-brown —Sorted, massive, 13 DAKOTA —Fine-grained organic matter (sapropel), may matter (sapropel), may —Fine-grained organic —Similar to unit unit to —Similar Holocene RAMSEY 12 —Mapped on steep bluffs along the Minnesota along the Minnesota —Mapped on steep bluffs 14 cannot be distinguished as either Heiberg or Villard Villard or cannot be distinguished as either Heiberg Late Pleistocene 10 —The units described below are the Heiberg, Villard, ), leading to deposition of the deltaic New Brighton Brighton ), leading to deposition of the deltaic New ANOKA Qno ISANTI —Massive, yellowish-brown to gray, medium- to coarse- to gray, yellowish-brown —Massive, Qnb RICE ACKNOWLEDGEMENTS 9 May be interbedded with peat and contain modern organic May be interbedded with peat and contain modern organic 11 6 DESCRIPTION OF MAP UNITS 3 ) north of the channel. Eventually, the lake drained through an drained through an the lake ) north of the channel. Eventually, SCOTT HENNEPIN fine- to medium-grained sand fine- Qnd river channels along the Mississippi and Crow Rivers. Generally Generally Rivers. channels along the Mississippi and Crow river finer- Typically coarsens with depth and contains scattered organics. in the floodplains and coarser-grained grained on higher elevation alluvium . modern stream channel. Coarse-grained grained sand and gravel with local minor cobbles associated with with local minor cobbles associated grained sand and gravel Anoka. Likely into glacial Lake flow meltwater Grantsburg-sublobe surrounding diamict through wave-washing the result of reworking along with deposition in a deltaic environment Anoka . of glacial Lake generated by all three New Ulm Formation members and reflects mixed members and reflects mixed Ulm Formation generated by all three New lithologic composition. longer part of the present day channel of the Crow, Mississippi, and Mississippi, and longer part of the present day channel Crow, channelized Deposited by formerly fast-flowing, Minnesota Rivers. and the ancestral Warren related to glacial River glacial meltwater sediment. Terrace and Mississippi Rivers. Crow differs compositionally in its scarcity of Superior-provenance material material compositionally in its scarcity of Superior-provenance differs carved meltwater 2). It is present where Grantsburg-sublobe (Table and Heiberg Villard and eroded valley River the Crow what is now . outwash—undifferentiated Ulm Formation Member deposits. New matter in post-glacial land surface depressions currently or formerly depressions currently or formerly matter in post-glacial land surface content greater table. Only sediment with organic beneath the water than 50 percent is mapped. It commonly underlain by organic-rich, Mapping clay. and silt, sand, fine-grained lacustrine, Epoch, Holocene Service (2014). from the Natural Resource Conservation modified was Peat. very fine- to medium-grained sand deposited in glacial Lake Anoka. Anoka. to medium-grained sand deposited in glacial Lake fine- very resulting from incorporation and/or erosion of both provenance Mixed deposits. Local silt lenses with and Grantsburg-sublobe Superior-lobe fluvial or glacial to adjacent where surface the near gravelly and depth, Anoka . sand facies of glacial Lake sediment. Fine-grained and Twin Cities Members of the New Ulm Formation. The youngest The youngest Ulm Formation. Cities Members of the New Twin and contains considerably higher amounts of shale the Heiberg, member, 17 (average Villard 41 percent) compared to the slightly older (average 13 percent) Members (Johnson and Cities (average Twin percent) and more contains also average, on Member, Heiberg The 2016). others, Members both represent Villard and The Heiberg material. fine-grained Cities Twin deposits, whereas the pure Riding Mountain-provenance Member represents both Riding Mountain- and Superior-provenance deposits. Unit deposits. where oxidized, dark gray (2.5Y 4/1) where unoxidized, lake sediment. sediment. where oxidized, dark gray (2.5Y 4/1) unoxidized, lake coarse-grained sand fraction is composed primarily of shale, The very The unit is mapped near Rogers, where grains are present. few but sublobe at the ice margin fronted the Grantsburg a proglacial lake indicated. Locally interbedded with small sandy lenses that indicate into the lake. small pulses of meltwater along the Crow River. This unit is texturally similar to unit This unit is texturally River. along the Crow Member sediment and is therefore undifferentiated, and unit Member sediment and is therefore undifferentiated, be both massive and laminated, fine-grained sand, silt, and clay in sand, silt, and clay in and laminated, fine-grained be both massive water. basins or other areas of non-flowing current or former lake gray-green-blue where unoxidized. to black where organic-rich, Brown wave- Includes macro-organics. other and shells mollusk contain May generated shoreline and beach sediments along with human-made ponded originated as water beaches. Most, if not all, of these lakes drained, was Where patterned, the lake in former ice-block locations. with other material. Unit is especially common and filled excavated, areas. Lacustrine deposits . in developed River and its tributary valleys. Unit consists of loose, redeposited Unit consists of loose, redeposited valleys. and its tributary River sediments from upslope ranging clay to boulders. Colluvium. loamy fine-grained sand that is common in floodplains in the Minnesota sand that is common in floodplains the Minnesota loamy fine-grained streams with a sediment Also present in small, low-flow valley. River material eroded from surrounding load dominated by fine-grained deposits . Fine-grained alluvium . material. Fine-grained 4 Very Sand and gravel Silty clay loam to silt Fine-grained sand to sandy gravel 8 7 LE SUEUR 5 —Partially decomposed, fine- to coarse-grained plant to coarse-grained plant decomposed, fine- detritus —Partially Organic —Fine- to coarse-grained sand and gravel occupying modern modern occupying —Fine- to coarse-grained sand and gravel Sand and gravel New Ulm Formation Terrace sand and gravel and sand Terrace
Organic clayey silt to sand clayey Organic Loamy sand and gravel Silty clay loam to loamy fine-grained sand Silty clay loam to loamy fine-grained New Brighton Formation CARVER SHERBURNE
As Grantsburg-sublobe ice continued to stagnate and calve into additional ice into additional ice ice continued to stagnate and calve As Grantsburg-sublobe Matthew Porter and Collin Giusti assisted in drilling auger holes in Hennepin Porter and Collin Giusti assisted in drilling auger holes Hennepin Matthew Additional meltwater from the drainage of glacial Lake Agassiz in northwestern in northwestern Agassiz from the drainage of glacial Lake Additional meltwater Each number of lakes. by a large Hennepin County is marked In addition to rivers, INDEX TO PREVIOUS MAPPING TO INDEX Ql 1 Qc Qp Qhl Qat Qas Qag Qnb Qnd Qno
Formation (unit Formation 1998). One meltwater channel in Golden Valley may have flowed to the north into to the north into flowed may have Valley channel in Golden 1998). One meltwater Anoka (unit glacial Lake slackwater lakes are common within the Minnesota River valley because the modern modern the because valley River Minnesota the within common are lakes slackwater Warren. formed by glacial River no longer occupies the entire width of valley river altered the landscape, especially on top that eolian (wind) activity It is also likely thicknesses of windblown no significant stagnation plains, but of former ice-walled Further alteration of the landscape post-glacially sediment (loess) were identified. resulted from industrialization and establishment of human society.
of interconnected lake bays/basins. of interconnected lake Anoka County to form to the northeast in into the lowland flowed blocks, meltwater YPB Anoka (Fig. 3E), which persisted until 13,650 to 13,550 cal glacial Lake orientation switched from perpendicular to the ice margin to ice marginal. This This to ice marginal. orientation switched from perpendicular to the ice margin Minnetonka position just east of Lake continued to recede a final parabolic ice margin point of this parabolic ice Minnetonka is situated at the vertex/focal (Fig. 3E). Lake together oriented east–northeast in the and the numerous bays of lake, margin, ice of Grantsburg-sublobe decay/erosion active indicate ice-flow, direction of former these ice blocks persisted for some time ice blocks. It is likely in the form of large These land basin. peninsulas and isthmuses within the lake by the many as evidenced between ice blocks that were subsequently filled or lows forms represent former gaps (unit sublobe Grantsburg the of melting the during surface on top of and interbedded with lake sediment (unit on top of and interbedded with lake surface County. Thanks are extended to the Three Rivers Park District, the Minnesota District, the Minnesota Park Three Rivers to the Thanks are extended County. Authority of Hennepin County, Railroad Department of Natural Resources, the Regional Department and Recreation Department of Edina, the Parks the Parks trails. bike along and parks their in drilling auger allowing for Center Brooklyn of Mooers, Alan Knaeble, Barbara Lusardi, Howard Additional thanks to Gary Meyer, Harold, and Meagan Retzler, Andrew Elizabeth Dengler, Amie Staley, Wagner, Kaleb Porter for their counsel during the construction of this map. especially Matthew area of north Minneapolis termed the Camden breach (Fig. 3F; Meyer and Hobbs, and Hobbs, area of north Minneapolis termed the Camden breach (Fig. 3F; Meyer terraces with numerous of wide river 1998), and led to the development 1989; Meyer, plains. and lake across the flat outwash braided streams that flowed Hennepin to the southeast, then turned northeast toward Minnesota flowed the (Fig. 3F), carved Warren called glacial River This deluge of meltwater, County. Warren (Wright, 1972). Glacial River of the modern Minnesota River valley large conduit in the state, with Mississippi River initially the dominant meltwater was and terrace level to a lower This restricted the Mississippi River acting as a tributary. terraces lacustrine deposits on higher outwash slackwater caused the formation of large it reached continued to entrench its valley, Warren As glacial River in Minneapolis. channel/ where it encountered a deeper former river St. Paul a point near downtown limestone (Wright, Formation atop Platteville and formed a waterfall bedrock valley Formation the Platteville The poorly cemented St. Peter Sandstone below 1990). blocks of limestone to collapse to erode, causing a chain reaction of large then began Snelling State Park. thinned just west of Fort Formation upstream until the Platteville the entered River Mississippi tributary where the a waterfall generated collapse This continued to erode Falls, Anthony as St. known This waterfall, valley. main river to Minneapolis, valley Mississippi River upstream to the north and deepen tributary Wright, 1990; Meyer, and Hobbs, 1989; establishing the modern floodplain (Meyer contemporaneously formed during the in Minneapolis was 1998). Minnehaha Falls as the already established Minnehaha Creek joined with Falls Anthony retreat of St. the volume valleys, the establishment of these river Following the Mississippi River. Minnesota. vacated decreased as all ice lobes finally of meltwater represents a former ice block or cluster of blocks left behind by the Grantsburg lake also controls the sublobe and/or the Superior lobe. Underlying bedrock topography a large in Minneapolis that overlies such as the chain of lakes orientation of lakes, area throughout decreased in surface of these lakes Many in the bedrock surface. valley post-glacial climate. In areas the Holocene Epoch, normal result of a warmer material (unit decreased, organic have levels where lake WRIGHT SIBLEY MCLEOD ) is ) is Data- Qtt ; Figs. ; Figs. Meltwater-channel orientations (3-foot orientations (3-foot Meltwater-channel Qts (Wright and and (Wright 5 and before the and before the 4 Figure 5. Figure At one point during the active [1-meter] lidar base). meltwater sublobe, two recession of the Grantsburg from the perpendicularly away channels flowed in blue (ticks on up-ice shown easternmost ice margin to the northeast side). One of these channels flowed The other Calhoun). into Bde Maka Ska (formerly Lake channel is the ancestral Minnehaha Creek (outlined). receded to the westernmost ice- Once this ice margin switched orientation meltwater-channel shown, margin The to parallel. from perpendicular to the ice margin bend sharp the generated margin ice this of recession in Minnehaha Creek. ORDOVICIAN QUATERNARY ) Members of the New Ulm Ulm ) Members of the New Qht Lake
Harriet (Clayton and Moran, 1982).
4 Pleistocene RAMSEY Holocene Bde ; Fig. 4A). The Twin Cities Member was Cities Member was Twin The ; Fig. 4A). ) composed of sediments incorporated from from incorporated sediments of composed ) Maka Ska Qti DAKOTA Qsi ANOKA Figure 4C Figure 4E Figure 5 Wisconsinan glaciation Figures 4A, B, D (Johnson and Mooers, 1998). Later, the Superior lobe the Superior lobe (Johnson and Mooers, 1998). Later, ) and Heiberg (unit ) and Heiberg INTRODUCTION 2 GLACIAL HISTORY GLACIAL Qvt (Meyer and Stefanova, 2009; Meyer, 2010) was determined determined 2010) was 2009; Meyer, and Stefanova, (Meyer 1 SCOTT HENNEPIN (Clayton and Moran, 1982; Mooers and Lehr, 1997), generating a 1997), generating a (Clayton and Moran, 1982; Mooers Lehr, 3 Bedrock New Ulm New Formation Cromwell Formation (St. Croix phase) New Brighton New Formation ). A total of 1,038 samples were analyzed for texture, lithology of the very lithology of the very A total of 1,038 samples were analyzed for texture, ). LOCATIONS FOR FIGURES 4 AND 5 FOR FIGURES 4 LOCATIONS CARVER Grantsburg-sublobe deposits have variable composition, especially in shale composition, especially in shale variable deposits have Grantsburg-sublobe The Twin Cities Member is absent or very thin in the subsurface along the along the thin in the subsurface Cities Member is absent or very Twin The sublobe, numerous retreat of the Grantsburg and active Throughout the advance The Superior lobe then began to actively retreat to the northeast starting at about retreat to the northeast starting at about to actively The Superior lobe then began Following the retreat of the Superior lobe, Hennepin County was glaciated for glaciated for the retreat of Superior lobe, Hennepin County was Following This map emphasizes the origin and distribution of the surficial geologic sediments geologic sediments of the surficial This map emphasizes the origin and distribution history a long reflecting complex, is Minnesota throughout geology surficial The Wisconsinan into Hennepin County during the late major ice advance The first Qp Qtl Qhl WRIGHT from wood underlying Superior-lobe deposits in Chisago County to the northeast. During underlying Superior-lobe from wood from the northeast and deposited sediments of this time, the Superior lobe advanced These include reddish lacustrine, till, (Johnson and others, 2016). Cromwell Formation (unit deposits ice-contact and outwash, Rubin, 1956; Clayton and Moran, 1982), an offshoot of ice from the Des Moines lobe, of ice from the Des Moines lobe, Rubin, 1956; Clayton and Moran, 1982), an offshoot As it advanced, sublobe, branched to the northeast (Fig. 3C). called the Grantsburg sediments, including freshly-deposited Superior-lobe sublobe overrode the Grantsburg kames. Fine- recessional tunnel valley multiple small terminal moraines and patchy of the Grantsburg the advance Lind facilitated grained sand deposits of glacial Lake that the There is also evidence an easily deformable substrate. sublobe by providing sediments lacustrine proglacial own its deformed and overrode sublobe Grantsburg near the terminus at Pine City moraine (Johnson and Hemstad, 1998), a process of the lobe. Once flank occurred throughout the advance that may have sublobe reached the up-ice side of St. Croix moraine, it encountered Grantsburg Dakota from extending moraine the of form relief higher and continuous more a unable Counties and was Washington and County to the northeast through Ramsey further. any to advance distinction the basis for the is areas adjacent and County Hennepin in which content, (unit Villard between the Formation. Evidence collected as part of this project suggests that the variability can can Evidence collected as part of this project suggests that the variability Formation. ice, the beneath substrate of incorporation of degrees the by for accounted largely be and comminution of material by ice deformation. In this scenario, initial high shale sublobe content (greater than 40 percent) of sediment in up-ice areas the Grantsburg Member as the Villard characteristic of the decreased by comminution to levels was Additional changes in sediment composition occurred as to the northeast. ice flowed Member, Villard carrying sediment characteristic of the sublobe, now the Grantsburg where it incorporated underlying further northeast through Hennepin County, advanced Cities Twin sediment of the provenance deposits, generating the mixed Superior-lobe 1980; (Figs. 4A, D, E; Stone, 1966; Chernicoff, Ulm Formation Member of the New Cities Member (unit Twin of the Till 2007). and Hobbs, 1989; Meyer, Meyer the underlying bedrock over which the lobe passed (Fig. 2; Table 1). An equilibrium An equilibrium 1). Table which the lobe passed (Fig. 2; the underlying bedrock over and melts at the same rate) of Superior lobe during position (when ice advances by buried in Minnesota because it was everywhere the Emerald phase is not evident appears the ice advance but expression, surface subsequent glaciations, or it has a patchy Superior the that likely is It 3A). (Fig. County Hennepin of most covered have to lobe), Wadena the called (also lobe Rainy the with contemporaneously advanced lobe and The Hewitt ice lobe, during this phase (Fig. 3A). a north–northeast provenance Wright County lobe occur in associated with the Rainy de Sioux Formations Traverse indicating that were not found in Hennepin County, to the west (Knaeble, 2013), but between the somewhere existed ice lobes must have the boundary between two both retreated, the timing of lobes eventually The Superior and Rainy counties. two have to been speculated has but age dates, radiocarbon constrained with is not which YBP occurred about 24,000 cal also generated where the Grantsburg sublobe encountered topographically high tunnel sublobe encountered topographically high tunnel also generated where the Grantsburg Minnetonka, Maple Grove, kames of the Superior lobe located in Greenfield, valley Hill neighborhoods of Minneapolis. and Lowry and the Bryn Mawr thick and little to sublobe, where the ice was former central axis of the Grantsburg Members are present in this and Heiberg Villard no erosion occurred. Instead, the deposited Member was Villard The deposits (Fig. 4C). Superior-lobe area overlying shale content low and thus maintained relatively ice flow, during continued active deposited late in the Member was produced by comminution. In contrast, the Heiberg It is associated with numerous ice waned. ice flow history of the sublobe, as active stagnation plains and ice-block depressions. stagnation features, including ice-walled minimal in these conditions; therefore the shale content of Comminution of shale was This interpretation of the content and distribution high. the deposits is comparatively Members is generally consistent with the Des Moines-lobe and Heiberg Villard of the from the suggestion of Lusardi and others (2011) model of Matsch (1972). It differs ice streams with shifting source areas played a more important role in that several Further research is needed to better variability. dictating compositional and textural of these processes. contribution understand the relative opening out to a broad channels incised proglacial sediments, eventually meltwater much of the eastern part Hennepin County (unit plain covering outwash readvanced into Hennepin County during the St. Croix phase. During the readvance into Hennepin County during the St. Croix phase. During readvance readvanced St. Croix moraine (Fig. 3A), of which the the extensive phase, the Superior lobe built to Hennepin County is along the northwestern border of expression closest surface and north west to the buried moraine was The St. Croix to the west. County Dakota it can be seen but Wright Counties by subsequent glacial advances, in Hennepin and The location of the St. Croix moraine in southeastern Stearns County. at the surface interpretation of Subsequent subsurface in Hennepin County is therefore unclear. Superior the moraine, large one forming of instead that indicates glacial stratigraphy lobe formed multiple smaller moraines, implying that this portion of the Superior Wright and Hennepin Counties fluctuated more than it did in adjacent in ice margin Counties. Stearns and Dakota 18,200 cal YBP the final time by ice of the Des Moines lobe. The Des Moines lobe advanced into into The Des Moines lobe advanced time by ice of the Des Moines lobe. the final and continued south to Des Moines, Iowa, Winnipeg northwestern Minnesota from 1). Table (Fig. 2; carrying rocks characteristic of Riding Mountain provenance members nine are there which of Formation, Ulm New the called are deposits Its After the and shale composition (Johnson others, 2016). distinguished by texture YBP Automba phase of the Superior lobe at 16,500 cal of the advance 3D, E). The orientation of these channels indicates initial meltwater flow away from or from or away flow The orientation of these channels indicates initial meltwater 3D, E). sublobe recession of the Grantsburg during the active perpendicular to the ice margin flowed channel perpendicular to this same ice margin Another meltwater (Fig. 5). the northeast. Once margin Calhoun) toward into Bde Maka Ska (formerly Lake up-ice, and meltwater-channel to convex retreated, it changed shape from concave preferentially distributed along the former margins of the Grantsburg sublobe, where sublobe, where of the Grantsburg along the former margins preferentially distributed and sheared incorporated underlying Superior- radially, flowed thinner, the ice was deformation under high stress gradients This process of ice-marginal lobe deposits. and is a well-documented phenomenon (Alley flow and longitudinally compressive of this deformation The most striking examples 2010). others, 1997; Benn and Evans, sediment located in Eden lake provenance are the push moraines cored with mixed Prairie, Edina, and Bloomington (unit wide, patchy network of coarse-grained outwash fan deposits at the mouths of tunnel tunnel of the mouths deposits at fan of coarse-grained outwash network wide, patchy proglacial 1994), and contributing as it receded (Mooers, 1989; Patterson, valleys landscape (Fig. 3B). Some of this meltwater to the freshly deglaciated meltwater deposits spots on the landscape up-ice from recessional Superior-lobe ponded in low Lind. Other meltwater sandy phase of glacial Lake and formed an early fine-grained coalesced and drained paths and eventually tunnel-valley existing followed likely ice numerous behind left lobe also Superior The River. Mississippi the ancestral into persisted likely blocks ice These landscape. vacated recently the around and in blocks by evidenced as County, Hennepin into advances glacial two final the throughout indicating an County, Washington ice-wedge polygons in the St. Croix moraine of the advance after conditions cold, continuous permafrost of very period extended the as known advances, final these of first The 2016). (Stanley, lobe Superior the content clay and silt higher with till Formation Cromwell deposited phase, Automba Lind sediments of proglacial Lake tills, implying reworking than older Superior-lobe south to north Minneapolis, and have Automba-phase deposits extend 1998). (Meyer, YBP been dated to be approximately 16,500 cal formation of glacial Lake Grantsburg between 14,400 to 13,900 cal YBP cal 13,900 to 14,400 between Grantsburg Lake glacial of formation in Hennepin County, Minnesota. It is a revision of the surficial map by Meyer and and map by Meyer of the surficial Minnesota. It is a revision in Hennepin County, well logs from the Minnesota Geological Hobbs (1989). Updated data include: new soil boring data from the Minnesota Department of new Index, Well County Survey digitized soil maps and data sets (National Resources Conservation Transportation, information, bathymetry digitized lake aerial photographic imagery, Service, 2014), new Additional (Fig. 1). and county-wide 3-foot (1-meter) resolution lidar coverage interpretation and analysis the in included was mapping previous from information in conducted fieldwork by augmented further were data existing These units. map of pits, gravel in exposures surficial limited at observations included that 2016 and 2015 hand auger borings construction sites, and road cuts, along with shallow excavations, These were supplemented by 150 auger borings to a depth of 5 feet (1.5 meters). 1, Plate see meters; (6 feet 20 of depth average an to probe soil Giddings a using Base Map All analytical results coarse-grained (1-2 millimeter) sand fraction, and Munsell color. data, this were digitized and compiled geospatially for mapping. In addition to new associated their and landforms glacial about interpretations new includes update map on the landscape, but made to account for human development was sediments. Effort sediments found at the surface. the map depicts pre-development generally, during the Pleistocene (2,600,000 to 11,700 years of glacial and post-glacial events the ago) and Holocene (11,700 years ago to present) Epochs. In Hennepin County, of the last glacial maximum Laurentide geologic units reflect the events surficial units is The interpretation of these glaciation. Wisconsinan Ice Sheet, named the by recognition of distinct ice lobes that each generated a unique assemblage facilitated This unique assemblage is controlled by the bedrock type and 1). of rocks (Table of the ice (Fig. 2). sediment in the source area, or provenance, age maximum a which for lobe, Superior the of phase Emerald the during was glaciation YBP of 32,547 ± 762 cal Ql Qvt Qtt Qht Qst Qsh CORRELATION OF MAP UNITS CORRELATION Qc Qtc RAMSEY COUNTY DAKOTA COUNTY 44°52'30" Qsi Qti Qhi T. 28 N. T. Qnb Ice margin Qas Qno Flow direction St. Croix moraine Meltwater Cities Twin Member deposits Member Villard deposits Heiberg Member deposits Glacial Lake Grantsburg deposits E' River ippississiM INDEX
45°
Qag F'
250
D' T. 29 N. T. 250 300
Prepared and Published with the Support of and Published with the Support of Prepared Qas 250
Qts Qat 275 Qag Qnd Qsi R. 23 W. Qts 6 31 6 6
225 31 55 Qtc R. 23 W.
250 Long )
RAMSEY COUNTY Ancestral St. Croix River
Ql WASHINGTON
Ql Qtt Ancestral THE HENNEPIN COUNTY BOARD OF COMMISSIONERS, THE HENNEPIN COUNTY BOARD
WASHINGTON Ancestral Qat
Qp 250 St. Anthony 250 35 W 49 4 § ¦ Qat § ¦ 1 CHISAGO CHISAGO Meadow 1 275 36 Mississippi River ANOKA 36 Mississippi River 1 T. 27 N. T.
COUNTY
Ql 225 moraine St. Anthony Falls, start St. Croix Qat Qc Qp Lake Lake Ql Hiawatha DAKOTA DAKOTA Edited by Lori Robinson Lori by Edited
Lake AND THE MINNESOTA LEGACY AMENDMENT'S CLEAN WATER FUND WATER CLEAN AMENDMENT'S LEGACY MINNESOTA THE AND 93°15' 77 93°15' )
St. Anthony Falls, today St.
RAMSEY RAMSEY
Nokomis 250 Camden breach 62 250 THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND TRUST RESOURCES NATURAL AND ENVIRONMENT MINNESOTA THE
) GIS compilation by A. Berthold A. by compilation GIS 250 Richfield 250 Qp R. 24 W.
Glacial Lake Anoka Glacial Lake ISANTI ISANTI ANOKA ANOKA Qag St. Croix moraine Ql Minneapolis R. 24 W. 250
T. 118 N. 118 T. 250 T. 119 N. 119 T. C' Qti 35 W § ¦
275 Qts B' HENNEPIN HENNEPIN 35 W SCOTT SCOTT 45°7'30" § ¦ 52 1 94 Qag 36 AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES, MINNESOTA ON COMMISSION LEGISLATIVE-CITIZEN THE BY RECOMMENDED AS ¤
Creek § ¦
25 2 250 Qp ) Ql
Qti
Grantsburg sublobe
250 Qat 250 Creek
275 Lake of the Isles GEOLOGIC ATLAS OF HENNEPIN COUNTY, MINNESOTA COUNTY, HENNEPIN OF ATLAS GEOLOGIC
250 SHERBURNE Warren River Glacial Qtt CARVER CARVER SHERBURNE Qag
Lake
Harriet
275 Qti LOCATION DIAGRAM LOCATION 275
Ska
Bde Qp
Maka
Qp
Qnb
- Qst - 39 4 Qp Brooklyn Center
§ ¦ 250 Palmer Lake WRIGHT WRIGHT Crystal Lake Qti
275
An example of streaky Twin Cities Member till from Edina. Cities Member till from Edina. Twin of streaky An example Qp SIBLEY SIBLEY
DAKOTA COUNTY Glacial Lake Grantsburg
275 Cities area deposits. Twin 4. Photos of the nature Figure of a push moraine in Edina. Note the A cut along strike A. nature of the sediments, reflecting mixed highly variable The Grantsburg composition and depositional environment. proglacial deposits and existing sublobe deformed its own push-moraine assemblages. deposits into complex Superior-lobe This road cut no longer Cities Member deposits. Twin TC: for scale. shovel exists; The of a push moraine in Edina. Another cut along strike B. sand and silty fine-grained bedding of proglacial outwash wavy emphasizes the deformed sand with microfaults fine-grained This road cut no longer exists; nature of these push moraines. for scale. shovel Member of the New Villard A sharp contact between the C. Anthony. near St. and the Cromwell Formation Ulm Formation deposits, the Despite being near the edge of Grantsburg-sublobe not generated, indicating that mixing Cities Member was Twin inconsistent. and incorporation of underlying sediments was coarse-grained sand Grain counts of the 1-2 millimeter very indicated contact the below and above taken of samples fraction tills at the contact. Samples slight mixing between the two very at and the contact was using a Giddings soil auger, were taken a depth of 17 feet (5.2 meters). D. The red color represents incorporated Cromwell Formation till. into Grantsburg-sublobe sediment (Superior provenance) but provenance, mixed reflects till the colorof brown overall The nature implies immature and incomplete mixing. the streaky Cities Member till from Golden Twin of the An example E. Cities Member is mottled, Twin of the This version Valley. tills. two the of mixing incomplete and immature showing till. Superior-lobe Des Moines-lobe till; ST: DMT:
Glacial Lake Grantsburg deposits
Qst
- Lake
275 Cedar -
-
- -
- -
- - - -
- Qat - Qp 6 31
MCLEOD
MCLEOD Ql
275 31 6 250 R. 21 W. SCOTT STEARNS STEARNS Minnehaha Qtl Qnd
275 Ql Qtl Ninemile COUNTY C.
F. Qti
Bloomington Ql Twin Lakes 250 Qtl 275 A' Qat Qas
Qtt 275 Brooklyn Park
10 0 Qts
Ql 52 ) Qvt Qtc 275 10 0 ¤ ) Ql
Ql 275 River ST Robbinsdale Ancestral St. Croix iver.
Crystal
Ql 275 Ancestral 55 Qnb WASHINGTON 275 WASHINGTON
)
275 Qtt Ancestral 275 275 250 275 Mississippi River CHISAGO CHISAGO Qat
275 250 R. 21 W.
Edina Mississippi River St. Louis Park DMT Qti moraine Hyland Lake Golden Valley St. Croix Qc 93°22'30" moraine St. Croix Qts
Qp 275 Qtl 275 93°22'30" 225
6
169 Qtc 275 Qag Qtt 31
¤ 275 DAKOTA
275 DAKOTA 94 6
Secondary carbonate 31 275 31 6 Qvt 31 § ¦ Anderson Lakes 6 Secondary iron oxide 31 6 RAMSEY Qp Ql
300 RAMSEY Meadow Lake
Qti 275
275 275 275 Qtc Qtt T. 115 N. 115 T.
Champlin New Hope T. 120 N. T.
Qtt 275 Osseo Qp 275 Outwash plain Lemans Lake 275 Lake Lind Glacial Lake Anoka ISANTI ISANTI ANOKA ANOKA Early glacial
275 Qti 36 169 Qp Qnd E. 275 Qti 169 ¤ 169 1 ¤ 1 1 36 1 ¤ 36 36 Lost Lake 36 Qts Ql Qp Superior lobe
Lake Qtt Eagle Lake Qtt Qp
River Hopkins Goose Lake Lake Qsi Hayden 275 5 MILES 250 Qp HENNEPIN HENNEPIN SCOTT SCOTT Qtl 8 KILOMETERS Medicine 300 Ql Ql Edward Lake Bryant Lake Pike Qvt Lake
Qp 275 Qti Qag Qti
Bass Lake 250 Cedar Island Lake
Qp Qvt 300 7
Plymouth
Powers
Lake 275 275 275 250 Minnesota 4 Qp CARVER CARVER
Qtc Mud
Qp Lake 275 Qti 300 300 Qts Qvt SHERBURNE SHERBURNE
Qtt 6 300 Qvt Qht Lake Ql Ql Medicine 49 4 275 300 Qas R. 22 W. § ¦ Ql
Mud Lake Creek Qtl
275 Qti WRIGHT WRIGHT Qti
49 4
Staring
300 3 Lake Lake § ¦ Qti 275 5 Qts R. 22 W.
Pomerleau 300 Qp SIBLEY SIBLEY
Glacial Lake Grantsburg deposits
Qas 275 275 275
300 325
Qvt 300 Grantsburg sublobe Eden Prairie Lake
300 Red Rock Plymouth 7 Purgatory Qp B. Grass Lake Rice Lake
Fish 300 Lake Des Moines lobe )
Qp Maple Grove
MCLEOD MCLEOD 275 Qht Dayton STEARNS STEARNS Qts Qsh Qsh Qsh 2
Qp Qp B. E.
Parkers Lake D.
275 Qp 300 Qtl 275
5 300 300
Qtt 250 3 4
Gleason
Lake Mississippi ) Qti
Qp 275 300 225 Qht
Weaver Lake 275 lacustrine Wayzata Qsh Qvt
Grays Bay TC SCALE 1:100 000
Lake French Qp 212 Lake Snyder
275
¤ 275
Qc TC outwash
Qp
93°30'
1 300 WASHINGTON WASHINGTON Superior 31 Qsh Qp Ql Ql 93°30' Ancestral lacustrine Minnetonka Lake Qht
Qp ANOKA COUNTY The Superior and Rainy lobes then retreated back to the northeast and north, respectively. The Superior lobe readvanced into Hennepin County during the St. Croix phase, including into into Hennepin County during the St. Croix phase, including The Superior lobe readvanced lobes then retreated back to the northeast and north, respectively. The Superior and Rainy Ql Qp
Diamond Qts - 300 CHISAGO CHISAGO 6 6
31 TC outwash Qp 31 31
275 6
Mitchell Lake
- 6 Mississippi River 31 6 275
1 2 CONTOUR INTERVAL 25 METERS 25 INTERVAL CONTOUR
300 moraine
St. Croix 31 275 - 300
Qts
- Qht
300 Rice 275 Lake Lake Riley Lake
300 Qhi Laura 0
DAKOTA DAKOTA COUNTY Ql
F Cromwell Formation
300 0 TC till 300 Qht 300
52
Qp RAMSEY RAMSEY
¤ 300 1
36 Qts Qp SHERBURNE
1 Lake - 1 Qhi Hamel
94 36 36
- SCOTT
275 300 36
WRIGHT Qp Qp Qht - § ¦ Christmas Lake 1 T. 116 N. 116 T. COUNTY
- COUNTY
Mooney CARVER COUNTY Superior lobe - 1 Qp
300 ISANTI ISANTI ANOKA ANOKA 44°52'30"
Holy Name Lake
Qvt 1 300 Qsh Lake Medina Qno
10 1 ) 275 Qhl
Lake Ql Qp
300 Albans St. Bay 300 Minnetonka Superior outwash Qp 55
HENNEPIN HENNEPIN Rogers SCOTT SCOTT ) 275 Lake Qp Long Qvt TC lacustrine 300 Wolsfeld Lake Qsh Qht Qp Qht
SHERBURNE CARVER CARVER 300 Cromwell Formation till Medina Corcoran SHERBURNE Excelsior Qsh Thies Lake TC outwash R. 23 W. Qp Qp
Qp 300 39 4 Qp Orono § ¦ Grantsburg sublobe WRIGHT WRIGHT Qht R. 23 W. Qp Villard Member Villard Qsh School Lake Lake Qsh Glacial Lake Grantsburg deposits Rainy lobe Lake Morin SIBLEY SIBLEY Peter Lake
Cowley
Qp Sylvan Lake 300 Scott Lake Qp Qht
Henry Lake 300 Thomas Lake Qp TC till Qht
Winterhalter Lake 300 Maxwell Bay MCLEOD MCLEOD
Crystal Bay
Spurzem Lake 300 Shorewood STEARNS STEARNS The Grantsburg sublobe actively retreated from its maximum position at the Pine City moraine to the position shown. It continued to flow radially, generating arcuate washboard moraines marking annual recession. Meltwater channels emanated channels emanated moraines marking annual recession. Meltwater generating arcuate washboard radially, It continued to flow retreated from its maximum position at the Pine City moraine to shown. sublobe actively The Grantsburg The stagnation of the Grantsburg sublobe generated the extensively ice-cored topography associated with the Heiberg Member of the New Ulm Formation in Hennepin County. Glacial Lake Anoka eventually drained through the Camden breach drained through the Camden breach Anoka eventually Glacial Lake in Hennepin County. Ulm Formation Member of the New associated with the Heiberg ice-cored topography sublobe generated the extensively The stagnation of the Grantsburg C. A. Qag
Qas Lake D. A. A schematic depiction of the late Wisconsinan glacial history of Hennepin County and surrounding areas. Wisconsinan A schematic depiction of the late 3. Figure lobe, Rainy with the contemporaneously advanced likely It (gray). Formation the Cromwell of sediment deposited and provenance) northeast (Superior the from phase the Emerald during County Hennepin into advanced first lobe Superior The A. of ice lobes is based on the existence The position of the dashed line separating two southern ice margin). (brown; Formation and deposited sediment of the Hewitt provenance) into Minnesota from the north–northeast (Rainy which flowed Wright County. sediments in adjacent Formation the Hewitt territory formerly occupied by the Rainy lobe, and deposited the St. Croix moraine (northern ice margin). This readvance ice margin is marked by thrust-block uplifts (hill-hole pairs) identified within the Lake Minnetonka basin, and is interpreted to Minnetonka basin, and is interpreted to within the Lake by thrust-block uplifts (hill-hole pairs) identified is marked ice margin This readvance lobe, and deposited the St. Croix moraine (northern ice margin). territory formerly occupied by the Rainy on the southern border of Hennepin that the portion of Minnesota River Area ski hill, another thrust-block uplift in Stearns County (Knaeble, 1998). During this phase, it is also likely Recreation Winter Ridge be contemporaneous to the Powder channel. meltwater County formed as an ice-marginal the ancestral coalesced toward deposits and eventually dissected recessional Superior-lobe the paths of former tunnel valleys, following Superior basin. Proglacial meltwater, the Lake After the St. Croix phase, Superior lobe retreated back toward B. Numerous ice blocks (gray) basin, a bedrock low. also controlled by the Stacy This ponding was Lind (dashed lines). ponded behind these recessional deposits and formed an early phase of glacial Lake Some of the meltwater Mississippi River. to the area. meltwater and contributed into Minnesota from the northwest (Riding Mountain provenance) Meanwhile, the Des Moines lobe advanced were left behind on the recently ice-free landscape, with a high concentration in Hennepin County. the ice-cored, dissected, and patchy radially over of ice flowed This offshoot sublobe. branched to the northeast from central core of lobe, forming Grantsburg into Minnesota, an offshoot As the Des Moines lobe continued to advance C. This the Mississippi River. toward and also flowed meltwater channels cut by Superior-lobe the existing in this area followed meltwater Grantsburg-sublobe terrain of the Superior lobe and as a result incorporated sediments provenance. Glacial Lake also deposited at this time in Hennepin County. Member till was Villard A central axis core of sublobe. of the Grantsburg along the margins particularly evident Ulm Formation, Cities Member of the New Twin generated the advance at this time. active to the north, was a proglacial lake Grantsburg, D. Croix St. the delineating area the of side southwestern the on Formation Ulm New the of Member Villard the of deposits exposed also position recessional This sediments. Member Cities Twin deposited recently into cutting margin, the ice from had drained by this time. Grantsburg Glacial Lake provenance. moraine. Because ice in this area did not cross the moraine, it is of mixed progressively channels emanated from this last ice margin, Numerous meltwater Ulm Formation. Member of the New Villard more sediments associated with the sublobe ceased and the ice stagnated, exposing recession of the Grantsburg Active E. the stagnant ice, ponds of Within Anoka. basin, forming glacial Lake to the northeast into Stacy the rest flowed but channels in southeastern Hennepin County, existing followed dissecting recently deposited material. Some of this meltwater stagnation plains. generating ice-walled formed on the ice surface, meltwater F. currently occupied by the Minnesota valley Warren glacial River in northwestern Minnesota also drained, forming the large Agassiz Glacial Lake terraces and delineating the modern path of Mississippi River. in north Minneapolis, cutting large Falls. Anthony also generated St. This deluge of meltwater River.
North Twin North Lake 300 Halfmoon Lake 300 Minnetonka Lake Qp Ql Jubert Qp Loretto Lake Katrina
93°37'30" 300
300 Qht 275 6 93°37'30" 31
31 300 Figure 6.2 — Ice Advances Affecting Hennepin County 6 31 31 6
Arm Qp Qag
Lake Ardmore 275 North Qno A West Arm West 325 300 Superior lobe advance and partial retreat and lake formation is followed by advance of an ice lobe from a different
Prairie Lake 300
300 Hillshade relief map of the 36
Qht 275 Qsh 1
1 direction. Broad meltwater streams deposited sand and gravel in southern Hennepin County as the ice in the interior 1 36 36 Independence Lake
300 300 300 Qp Maple Plain 36 Mound
Cook's Bay of the county stagnated before the Minnesota River valley formed (from Berthold, 2018).
Lake 300 Qp Schendel Schwappauff Lake T. 120 N. T. 300 1. Figure 30- County; Hennepin in surface land 1-meter from resampled DEM, meter sun angle of 30°; lidar data with a false ranges from azimuth 315°. Elevation 367.2 to (183.3 feet 1,204.69 to 601.5 = 5x. exaggeration Vertical meters). Hafften Lake Qht 300
Qvt River Qsh ! Qno
Qp
Superior 300 Langdon 300 Lake
300 300 Provenance
300 Qp 300 !
300 Richfield Dutch Lake Dutch 325 ! Qti St. Anthony 14 | Hennepin County Landslide Hazard Atlas Greenfield Halsted Bay
Minneapolis Qts
—Arrows point downstream in the in the point downstream —Arrows
! Rainy 300 300 ! Lake Sarah Qp Crow Qht Bloomington Qvt
Provenance
Golden Valley Edina Independence 300 Qag 300 St. Louis Park Irene Lake Qp Qp ! ! !
R. 24 W.
300 300 Rainy lobe Rainy
300 ! 300 Osseo Qvt —Broad, relatively level plateaus in areas of plateaus in areas of level —Broad, relatively ! Qht Brooklyn Center R. 24 W. Hopkins 7 ! Pre-Wisconsinan
)
Lake Medicine Lake Robina !
sublobe
Lake St. Louis St. !
!
! Qht
B ! Rattail Lake lobe Superior ) and cored by Twin Cities Member ice-contact Cities Member ice-contact Twin ) and cored by Eden Prairie sublobe ! 45°7'30" ! ! ! locally depending amount of variation ) with a large
! ! ! Champlin !
! ! Grantsburg ! ! Qp
! MAP SYMBOLS Whaletail Qtt Minnetonka ! —Hachures on the downslope side indicate the flanks flanks the indicate side downslope the on —Hachures
! Qti
!
Rebecca !
300 !
Lake ! 300 ! Wayzata ! COUNTY T. 119 N. 119 T. T. 119 N. 119 T. !
! ! ! ! Qp ! ! ! !
! HENNEPIN ! ! ! ! ! ! ! ! ! 300 ! ! ! ! ! ! ! ! ! ! ! ! !
Plymouth !
! ! ! ! !
! ! ! ! ! ! 12 300 Rogers moraine ¤ St. Croix ! Maple Grove —A former equilibrium position of an ice lobe marking either —A former equilibrium position of an ice lobe marking either
300 300 Qht ! Qas —Undifferentiated limestone, shale, and sandstone exposed along along limestone, shale, and sandstone exposed —Undifferentiated Orono
275 ! Qno 93°45' subglacial tunnel channel/valley or ice-walled channel by flowing channel by flowing ice-walled or subglacial tunnel channel/valley direction. Locally reworked indicate interpreted flow Arrows water. by anthropogenic activities. The feature is aligned with and eskers. hosts both chains of lakes Hachures point downslope. in the bedrock surface. valley a buried Interpreted to be a subglacial drainage channel of the Superior lobe. during subsequent glacial Other channels (not indicated) were filled events. Ox Yoke Lake Yoke Ox on the type of St. Croix-moraine deposit that was reworked (such (such reworked on the type of St. Croix-moraine deposit that was diamict, or lacustrine deposits). as sand and gravel, deposits (unit to concave up-ice ridges that represent deformation of proglacial up-ice ridges that represent deformation of proglacial to concave lacustrine sediments and St. Croix-moraine deposits by the Grantsburg Cities Member Twin sublobe (see Fig. 4A). Generally capped by diamict (unit the furthest extent of the lobe or recessional positions during ice of the lobe or recessional positions during ice the furthest extent and of sand Composed primarily of till with local pockets retreat. in the southwestern portion of county The ice margins gravel. indicate the multiple, smaller terminal moraines generated by All other ice margins Superior lobe during the St. Croix phase. These sublobe. Grantsburg the of positions recessional represent moraines in the northern part of county. include washboard are on the up-ice side of line. Ticks of former channelized meltwater flow. These channels were used These channels were used flow. of former channelized meltwater Ulm of the New diamict-depositing events repeatedly during various Formation. hummocky topography. Predominately composed of diamict with Predominately composed of diamict with topography. hummocky thickness in ranging loam silt with interbedded or of caps patchy from 1 to 9 feet (0.3 3 meters). Plateau relief ranges 10 more than 100 feet (3 to 30 meters) and reflects the former thickness of the stagnant ice. direction that glacial meltwater flowed. direction that glacial meltwater been incised by banks of former fluvial channels; interpreted to have are on the downslope Ticks glacial rivers. high volume flowing, fast side of the line. age. See Plate 2 for a more of Ordovician the Mississippi River detailed description. 93°45'
275 6 31 6 31 300 325 Winnipeg
Qp 31
Haughey Lake Des Moines lobe Provenance
Excelsior Qht 300 Qvt
300 St. Bonifacius Geologic contact —Approximately located. and sand deposited in a —A sinuous ridge of cobbles, gravel, Esker that locally —A broad trough in the modern land surface valley Tunnel Ice margin Ice-walled stagnation plain —Tall (50 to 150 feet [15 to 45 meters] of relief), linear linear relief), of meters] 45 to [15 feet 150 to (50 moraine —Tall Push General flow direction of meltwater direction General flow Meltwater channel Meltwater —An abrupt change in elevation (escarpment) marking the the marking (escarpment) elevation in change abrupt —An scarp Terrace Outcrop Qp
300 ! Digital base modified from the Minnesota Department of of Department Minnesota the from modified base Digital by annotation base digital data; BaseMap Transportation Survey. Geological Minnesota the Elevation contours were derived from the U.S. Geological Survey Minnesota the by (DEM) Model Elevation Digital 30-meter Survey. Geological 15 zone grid Projection, Mercator Transverse Universal Datum American 1983 North - Maple Plain C D Greenfield E !
! ! -- Independence Minnetrista 45°
Rockford - ! Riding T. 118 N. 118 T.
St. Bonifacius WRIGHT COUNTY CARVER T. 117 N. 117 T. COUNTY -
Location of major provenances and the distribution and the distribution 2. Location of major provenances Figure Distinct Minnesota. in surface land the at materials ice-lobe of from the unique assemblages of glacial sediments are derived suite of bedrock and sediment found in each the source regions from Riding Mountain Sediments derived shown. (provenances) of Rainy- extent The surface in green. are shown provenance and pink, in brown sediments is shown and Superior-provenance by the dotted line. The St. Croix moraine is shown respectively. direction. indicate primary ice-flow Arrows ! Mountain
- Provenance
- MINNESOTA GEOLOGICAL SURVEY GEOLOGICAL MINNESOTA Thorleifson, Harvey Director Minnesota of University the of Regents by the ©2018 educator and employer is an equal opportunity Minnesota of University The Valley Formation Failure Style in the Exposed and Destabilized Minnesota River Valley Sediment Layers and Tributaries The Minnesota River valley was created by the The largest failures in the Minnesota River valley draining of Glacial Lake Agassiz approximately are deep rotational failures with deposits that show 13,400 years ago. Immediately after valley formation, some evidence of liquefaction and flow. They are the valley walls would have been highly unstable. primarily located along the Minnesota River valley This is the likely time that the largest landslides in Bloomington. The lake sediment associated with occurred. If landslide activity was concurrent with the Superior lobe (Qcl) is present in the subsurface the river occupation, the deposits would have in these areas (Figure 6.4). Layered clay and silt been swept away by the glacial lake flood waters. impedes the downward movement of water, If they occurred after the flow subsided, landslide allowing it to build up porewater pressure on top deposits should be visible unless they have been of the unit and within the silt beds. buried by the sediment that has accumulated in the Springs emerge from the bluff at different Minnesota River valley since it was formed. elevations and indicate the horizons where water The valley cut 230 feet (70 meters) deep into the is accumulating and able to move laterally. Along landscape. This created waterfalls or steep reaches the slopes of the Minnesota River valley below East (knickpoints) at the mouths of the tributary streams. Old Shakopee Road and above Long Meadow Lake These knickpoints have been migrating upstream in Bloomington, there is a double spring line. The as tributaries continue to adjust to the base-level upper spring line, at an elevation of about 770 feet fall. In this way, over the last several thousand above sea level (ASL), is depositing iron. The lower years, the lower few miles of tributary valleys have spring line, at about 720 feet ASL, is depositing incised deeply enough to reach equilibrium with tufa, a form of calcium carbonate (Brick, 2018). These the elevation of the Minnesota River valley floor. two distinct spring lines most likely emerge from However, the tributary valley walls are young and contacts between units with different chemistry. upstream areas are continuously being destabilized The upper, iron-rich spring horizon may demarcate as knickpoints continue to migrate and new the top of the Cromwell Formation lacustrine clay knickpoints form in the tributaries. The deep reaches and silt (Qcl). The lower calcareous horizon is more of these valleys will continue to expand upstream consistent with the Meyer Lake Member of the Lake until the entire basin has adjusted its gradient. Henry Formation (Qh2). However, the Meyer Lake Where incision has happened most recently, near Member seems to be more deeply buried here. An the knickpoints, the slopes are most vulnerable alternative explanation for the difference in spring to failure. chemistry might be the variability in the Twin Cities Formation layers. Whatever the source of the Tributaries in the process of adjustment, and springs, these hillsides have the largest rotational therefore carrying as much sediment as they can failures in the Minnesota River valley. The springs handle, deliver it to the Minnesota River that is remain active, and arcuate cracks on the surfaces not effective at carrying it away. Major tributaries above the bluffs in this area are indicative of deep- have built fans at their mouths that contribute to seated landslides of unknown age that extend the overall aggradation of the valley floor. Modern 650 feet (200 meters) into the flat area beyond the sedimentation rates on the floodplain are on the bluff edge (Figures 6.5a, 6.5b and 6.5c). The different order of a centimeter or two per year (under an glacial units involved in the slides are interpreted inch) and much of the valley is filled with over from slide locations and nearby cross sections 50 feet (15 meters) of sediment (Jennings et al., 2018). produced by the MGS (Table 6.2, Figure 6.4). This is the process that has the potential to bury or obscure early landslide deposits.
Minnesota River Valley Landslides | 15 Table 6.1 Glacial and Postglacial Stratigraphic Units in Hennepin County (in order of ascending age)
Post-glacial Glacial Afhl Artificial fill over Holocene lacustrine Qno New Ulm outwash Aftci Artificial fill over Twin Cities ice-contact Qts T win Cities sand (the surficial version Afsi Artificial fill over Superior ice-contact of TC sand) Ql Holocene lacustrine Qhl Heiberg lacustrine Qas Fine alluvium Qhi H eiberg ice-contact (changed it to Heiberg; was Villard ice-contact on surficial map) Qag Coarse alluvium Qsh Heiberg stagnation Qc Colluvium Qht Heiberg till Qat Terrace sand Qvs Villard sand Qlt Lacustrine under terrace sand Qtc Twin Cities colluvium Qnd New Brighton delta Qtl Twin Cities lacustrine Qnb New Brighton sand Qst Twin Cities stagnation Pre-last glacial units Qvt Villard till Qh1 Sauk Centre outwash Qts2 Twin Cities sand within (not surficial) Qsc Sauk Centre till Qti Twin Cities ice-contact Qf1 St. Francis outwash 1 Qtt Twin Cities till Qsf1 St. Francis till 1 Qts1 T win Cities sand below till (Hillside sand equivalent) Qh2 Meyer Lake outwash Qms Moland sand Qml Meyer Lake till Qmt Moland till Qf2 St. Francis outwash 2 Qsi Cromwell ice-contact Qsf2 St. Francis till 2 Qs1 Automba phase outwash Qwo Old Rainy outwash Qca Cromwell till — Automba phase Qwt Old Rainy till Qcl Cromwell lacustrine Qeo Elmdale outwash Qs2 St. Croix phase outwash Qet Elmdale till Qcs Cromwell till — St. Croix phase Qvo Old Superior outwash Qs3 Emerald phase outwash Qost Old Superior till Qce Cromwell till — Emerald phase Qsu Q uat sand below old Superior-provenance till; unnamed Qu undifferentiated sediments
16 | Hennepin County Landslide Hazard Atlas Prepared and Published with the Support of COUNTY ATLAS SERIES THE HENNEPIN COUNTY BOARD OF COMMISSIONERS, ATLAS C-45, PART A MINNESOTA GEOLOGICAL SURVEY Hennepin County Harvey Thorleifson, Director THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES, Plate 5—Sand-Distribution Model AND THE MINNESOTA LEGACY AMENDMENT'S CLEAN WATER FUND
N SAND-DISTRIBUTION MODEL
By
LOCATION DIAGRAM Angela J. Berthold and Richard S. Lively
Surface Topography 2018
SAND AND GRAVEL BODIES
HENNEPIN WRIGHT ANOKA SHERBURNE CARVER SCOTT
Peat Qp hp Qp Qp pe sc TILL AND FINE-GRAINED SEDIMENT Qp Lake sediment Ql hl Qll Ql Qm Ql lb
Alluvial fan sediment af Qf
Alluvium Qas ha Qa Qa ss al Qa Al INTRODUCTION Each water-well record describes the vertical sequence of earth materials at the location of the REFERENCES Holocene Qag sediment well. Glacial till is generally described as "clay" by well drillers, and although sand and gravel The Quaternary sand and gravel deposits of Minnesota are the products of a long, complex Knaeble, A.R., 2013, Quaternary stratigraphy, pl. 4 of Tipping, R.G., project manager, Geologic Qvs Colluvium Qc co Qc can occur within a till, more extensive deposits tend to occur at the contact between two till layers. atlas of Wright County, Minnesota: Minnesota Geological Survey County Atlas C-30, 6 pls., glacial history that makes the subsurface mapping of these potential water-bearing units (aquifers) Where two clay (till) layers related to different depositional events were not separated by a sand Eolian sediment Qe Qe ss Qe scale 1:100,000. difficult. Establishing the location and characteristics of these sand and gravel units, however, is layer, their contact was recognized by a change in the driller's description of the clay's texture (for Terrace sand Qat wmt Qt Qwl Qwr Qtl Qtu ss tg tl tr Qts Qtg Qtl Qtr an essential step toward identifying aquifers and ensuring their appropriate use and protection. It is example clay/sandy, clay/clay, and gravel), density, or color. In general, the more detailed logs in Lusardi, B.A., 2009, Quaternary stratigraphy, pl. 4 of Bauer, E.J., project manager, Geologic atlas Lake sediment also useful for mapping potential aggregate resources. In Hennepin County, this project employed Qlt Qwf Qwc any particular area were given more weight by the geologist in drawing unit boundaries. Using the of Carver County, Minnesota: Minnesota Geological Survey County Atlas C-21, 5 pls., scale beneath terrace sand a process that combined the understanding and expertise of a geologist and a geologic information available data, contact lines were drawn along each cross section, with each line representing the 1:100,000. specialist with the data-handling capability of a geographic information system (GIS) to create Sand and gravel Qnd Qbg Qbg base of a unit of sand and gravel or till. GIS software was used to extract elevation values from ———2013, Quaternary stratigraphy, pl. 4 of Lusardi, B.A., project manager, Geologic atlas of Qvt New Brighton nbs three-dimensional models of Quaternary sand and gravel bodies. The distribution of sand and gravel Qnb nls Qbs vertices along each unit line and convert those into a gridded surface by interpolating the elevation Sherburne County, Minnesota: Minnesota Geological Survey County Atlas C-32, 5 pls., scale Formation Sand Qbs Qbt at the land surface was mapped by the geologist from exposures, shallow auger holes, soil maps, data. The resulting raster data sets represent the distribution of the geologic units over the county 1:100,000. Silt and clay Qbc landforms, and previous geologic maps (see Plate 3, Surficial Geology). In contrast, interpreting sand in three dimensions. Till surfaces were iteratively modified until the geologist was confident that Lusardi, B.A., and Tipping, R.G., 2006, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., project distribution in the subsurface relied primarily on well records, scientific drill core, and drill cuttings they adequately represented the stratigraphic interpretation for the majority of the water-well data manager, Geologic atlas of Scott County, Minnesota: Minnesota Geological Survey County dz (see Plate 4, Quaternary Stratigraphy, Fig. 1 and cross sections for locations). Sand-distribution Stagnation facies in the county. A similar process was followed for the surfaces of the sand and gravel bodies to Atlas C-17, 6 pls., scale 1:100,000. models are based on the assessment of these data, consideration of the processes that deposited the Ice-walled lake sediment nlc Qns Qnl ensure they conformed with till and water-well data. After both till and sand surface grids were Meyer, G.N., 2013, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., project manager, Geologic ns glacial sediment, and an understanding of the glacial history in the county. Despite basing these complete, they were processed through GIS raster calculations to create a set of top and bottom Glacial Lake Qng models and interpretations on the best available data, they are incomplete in some areas because of atlas of Anoka County, Minnesota: Minnesota Geological Survey County Atlas C-27, 6 pls., Grantsburg sediment surfaces and a thickness for each geologic unit. The result is a three-dimensional geologic model a lack of data. As a result, unit extent, thickness, stratigraphic correlation, and even the material scale 1:100,000. Outwash of tills and sands for the county. Qno ng nhs sd Qdo S1 of buried units may not be as well constrained as for the surficial units. The geologic model should be considered a guideline for the occurrence and approximate Lacustrine Qhl dl The unconsolidated Quaternary sediments that overlie the bedrock in Hennepin County are highly thickness of major sand bodies. The model does not guarantee sand and gravel will be found at all sdi variable in character and thickness. These deposits are largely the result of numerous, distinct ice Heiberg Ice-contact Qhi places shown, nor does it preclude them being found where they are not shown. It does indicate Member advances during the Pleistocene Epoch (see Plate 3 and Plate 4, Fig. 2). Most of the aquifers within Qts, Qts2, Qti Stagnation Qsh where sand features with large areal extent and significant thickness are likely to be encountered. the Quaternary section consist of sand and gravel deposited by proglacial or subglacial meltwater. Where data are limited, for example where wells end in a Quaternary sand and gravel unit, geologic Till Qht ht hbt htw dtc dth Qd Qds Qdc T1 Layers of unsorted sediment composed of clay to boulder-sized particles (diamict) interpreted to interpretations relating to the extent of sand and gravel bodies and their thickness tend to depict less Qvs Villard Sand nts sdv have been deposited directly by glacial ice (till), as well as fine-grained, bedded sediment deposited material than may actually be present. Additionally, erosion by ice and meltwater during subsequent CONTOURS FOR FIGURES DEPTH FOR FIGURES New Ulm Member Qvt vt nt vtw dtv into ponded proglacial meltwater, form low permeability confining layers (aquitards) that enclose the Formation Till Qnt Qna Qdl T1 glacial events may have removed portions of older sand bodies. Where incomplete data did not 3 THROUGH 15 5 THROUGH 15 aquifers. The till layers left behind by each ice advance tend to be laterally continuous because glacial Outwash Qts allow for stratigraphic interpretation, sediments were categorized as Pleistocene undifferentiated Thickness of a geologic 0–50 tco Qsl Qno ns S2 ice usually covered the entire county. Glacial meltwater is capable of producing large, extensive Qts2 deposits (unit Qu). This includes sand bodies (unit Qsu) that could not be assigned to a specific unit contoured at 20 foot (6 Qtt, Qst Sand deposits like outwash plains, but it can also generate more localized deposits in channels or basins glacial advance. In general, at increasing depths in the stratigraphic section, data availability meter) intervals. 51–100 Qtc Colluvium at the lower elevations of the landscape. In addition, glacial meltwater is capable of depositing diminishes and delineated units could be more or less discontinuous than shown. Any west to east 20 Depth in feet from the land Lacustrine Qtl sand and gravel during both the advance and the retreat of a glacier within one glaciation. As a patterns on Figures 5 through 16 are an unavoidable artifact of cross-section creation and digital 101–150 Twin Cities result, glacial till from an ice advance may bury sand and gravel associated with the same advance 40 surface to the top of a sand Member Stagnation Qst processing. Despite these limitations, the geologic model provides a realistic interpretation of 60 and gravel unit (depth from and/or sediment deposited during a previous glacial event. At the same time, a glacier is capable of where and what kind of geologic units lie in the subsurface of Hennepin County. However, given 151–200 Ice-contact Qti Qni Qdi 80 the land surface to the top of deforming, eroding, and incorporating the underlying substrate. The net result of each glaciation, the limitations of the data, the model should be used as a guide and should not preclude further Qtt nt Qnd 100 undifferentiated sediment is Till tct Qnt Qnc nt Qdt T2 given all of these factors, is a highly disturbed, discontinuous stratigraphy with complex cross-cutting site-specific investigations or inspection of individual well logs. 201–250 Qts1 relationships (Fig. 1). By convention, the depicted sand and gravel bodies are named after the till 120 shown on Figure 15). Sand below till Quaternary deposits in Hennepin County are listed in stratigraphic order along with equivalent underlying them, but exceptions were made for those at the land surface, above undifferentiated 140 251–300 units from adjacent Wright (Knaeble, 2013), Anoka (Meyer, 2013), Sherburne (Lusardi, 2013), Sand Qms ms sediment, and where data were sufficient to make that determination. 160 Moland Carver (Lusardi, 2009), and Scott (Lusardi and Tipping, 2006) Counties in Figure 2. The more 180 301–350 Member Till Qmt mt Qdd T1 In order to model this stratigraphy, 103 cross-section lines spaced 0.3 mile (0.5 kilometer) extensive sands portrayed by the geologic model are shown in Figures 3 through 15, ranging from 200 Prepared and Published with the Support of COUNTY ATLAS SERIES apart were generated in a west–east direction (Plate 4, Fig. 1). The results from the cross-section Prepared and Published with the Support of COUNTY ATLAS SERIES THE HENNEPIN COUNTY BOARD OF COMMISSIONERS, ATLAS C-45, PART A the youngest sands at the land surface to buried, progressively older sands (Fig. 1). A number of MINNESOTA GEOLOGICAL SURVEY351–400 Qs2 THE HENNEPIN COUNTY BOARD OF COMMISSIONERS, 220 and greater ATLAS C-45, PART A THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND Hennepin County cg MINNESOTA GEOLOGICAL SURVEY analysis are available digitally as raster data sets for the top and bottom elevation surfaces and Harvey Thorleifson, Director Ice-contact Qsi Qci Qci csr Qci factors determine whether or not the sand and gravel units depicted here are usable aquifers. To be Hennepin County AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES, Plate 4—Quaternary Stratigraphy Harvey Thorleifson, Director thickness of each interpreted unit of till and sand. Examples of these interpretations along six of THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND Note: Contour lines may not close at an aquifer, the units must be saturated and able to readily transmit water to a well. Their capacities Plate 5—Sand-Distribution Model AND THE MINNESOTA LEGACY AMENDMENT'S CLEAN WATER FUND Outwash Qs1 csa AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES, the edges of mapped areas. This is these lines are shown in cross sections A–A' to F–F' on Plate 4. Along these lines, descriptions A Crow River Henry Lake Interstate 94 Elm Creek Lemans Lake U.S. Highway 169 Mississippi A' Automba AND forTHE water MINNESOTA storage andLEGACY transmission AMENDMENT'S depend onCLEAN their WATERextent andFUND thickness, as well as factors such 1,000 Qhl River Till Qca an artifact of the digital processing. k phase and samples from a combination of water-well records, rotary-sonic core, engineering test holes, Qno k Qlc as sediment coarseness, degree of sorting, consolidation, and potential for recharge. Connectivity 950 Figure 1. Location of 103 west–east cross sections, constructed at k cta kk Qht kkkkkk Ql regular 0.3-mile (0.5-kilometer) intervals, used to create a three- k kkk Lacustrine scientific cutting sets, and auger borings (Plate 1, Data-Base Map) were used to identify contacts Ql Qht k Dayton k kk Qcl Qvs Ql k k kk Cromwell between the sand and gravel units is also important. In many places, two or more sand and gravel 900 SCALE 1:300 000 Ql Qs1 dimensional model of the Quaternary deposits of Hennepin County. k Qvt k kk Qml Qht Qas Qtt k Qs2 Qcs Qs2 Qag The locations of cross sections A–A' through F–F' are shown here Qts1 Qat k kk k k Formation between units in the subsurface. The geologist provided an interpretation of materials that occur 850 Qs2 Qtt Qs2 Qca Qvs kk Qco Qsc Qml Qf2 Qs2 Ql Ql and are also on Plate 3, Surficial Geology. Black squares indicate the k Qs2 cg Qco csr units may connect to form a single aquifer if there is no intervening till layer. Water quality also 5 0 Qf2 5 Qcs 10 MILES Ql Qca k Outwash s Qs1 Qs2 HS-4 k St. Croix j k kk k QUATERNARY STRATIGRAPHY Qcs Qeo Qet j Qvo Qml Qf2 Qs2 Qht Qca locations of the five rotary-sonic core samples collected for this study. A A' in the areas between data points or at depths not penetrated by drill holes based primarily on an 800 Qeo Qs2 Qcl k s Qvt k phase tm s Qs3 Qcs Blue asterisks indicate the locations of the 19 archived split-spoon core k k determines whether an aquifer is suitable as a source of drinking water. The maps and reports j Qsf2 Qvo Qcs Qh2 k k k Qcs Qs3 k k Till ct Qcr Qct Qcd ctr tl Qot Qs1 s k kk k 5 0 5 10 KILOMETERSs Qml Qs3 Qs2 s holes analyzed for this project. Site names are listed. Black asterisks k k k k 750 tmQsu Qvo tm Qf2 tm s j Qs3 k k k understanding of geologic processes. tm tm kk tm indicate the locations of 459 borings where drill cuttings were collected k k k produced by the Minnesota Department of Natural Resources, as Part B of this County Geologic Qsf2 tm k kkkk Greenfield kkkkk k kk k By Qse N 700 s j and described for this study. kkkk k k k kk k kkk Emerald Outwash Qs3 cg1 cse sr tl tl k k k k kkk s kk kk kkk k kk Qsf2 tl B kkkkkk k k k k B' Qeo Qet k Corcoran k k k k k Atlas, take these and other factors into consideration to characterize hydrogeologic conditions. tl j k LOCATION DIAGRAM SAND-DISTRIBUTIONtl MODEL k k phase 650 k k tl k k k Elevation (feet above sea level) k Qce cte Qet k k k Angela J. Berthold Till ct1 Qce rt Qvo k k kk k w k k k 600 w k k tl k k k kkkkkk k C kkkk k k C' w k kkkk w Independencek k k 550 k k k tm k k 2018 k k k kkk k k k k k k By k k k k k k k k kk k k k hs k k k kk Outwash 500 k k k k k k Hewitt kk k k k k k k kk kk k HS-3 k k k Formation k kkk k 93°30' 93°30' k k hwt B B' kk k k Till k k k k k 1,100 k kkk k County AngelaRoad 19 J. Berthold and Richard S. Lively k k k k kk LOCATION DIAGRAM Crow River County Road 10 D k k k k k k k D' k k kk k kk k k k k k k k k k k k 1,050 k k R. 22 W. Ql k k k R. 23 W. R. 23 W. R. 22 W. k k k k k k k k Borehole name: HS-1; unique number: 277941 Borehole name: HS-2; unique number: 277942 Borehole name: HS-3; unique number: 277943 Borehole name: HS-4; unique number: 277944 Weaver Lake Interstate 94 Rice Lake County Road 81 U.S. Highway 169 State Highway 252 Mississippi k sb Qvs k k k k k Outwash 1,000 Qht k k kk k kk Location: T. 28 N., R. 24 W., sec. 9; BBBBBB Location: T. 117 N., R. 23 W., sec. 28; CDAAAB Location: T. 118 N., R. 24 W., sec. 28; BCCCCD Location: T. 120 N., R. 23 W., sec. 9; BDDCCC Ql River k k kk kk HS-1 Browerville kk k 93°37'30" 93°37'30" Qno k k k k k Elevation in feet above mean sea level: 854 Elevation in feet above mean sea level: 940 Elevation in feet above mean sea level: 955 Elevation in feet above mean sea level: 1,017 Surface Topography Ql 2018 E k k k k E' k k Qcs Ql k Formation 950 Qvt Qs2 Qvt k HS-2 Depth Lithology Unit Description Depth Lithology Unit Description Depth Lithology Unit Description Depth Lithology Unit Description )101 )101 Qs2 k k k k k bt k Till Qs2 Qcs Qvs k k k k (feet) (feet) (feet) (feet) T. 120 N. Qs2 T. Qsc120Qcs N. Qvt k k k kk k k k kk k k 0 Ql 0 0 0 900 Qsc Qsc Qht Qht k k Dark grayish-brown silt and silty sand interbedded Olive-brown fine- to medium-grained sand; slightly Light olive-brown silty very fine-grained sand; calcareous; fines Qf1 Qsf1 Qs3 Qcs Qs2 k k k k Olive-brown to 19', very dark gray below, loamy diamict; leached Qf1 Qvt k k k k with peat; upper 7' anthropogenically disturbed; Qsf1 Qh2 Qsc Ql Qnd k kk kk calcareous; contains organic debris no larger than cobble- to a depth of 1.5', calcareous below; massive; contains minor Qhl upward; generally massive with some bedding in the lower 1.5'; Ql Qat Ql k k k Ql Qml Qf2 Qf1 Qs2 Qsi Qag k k evidence for natural lacustrine deposition after -10 sized; backfill in a former gravel pit—artificial fill contains large manganese stain at a depth of 3'—lacustrine 850 Qml Qml Qs3 Qtt kk k -10 sand seams from 0-31' and from 47’-51.5'; contains shale and Qh2 Qsf2 Qsc Qcs Qts Qat kk k k Qag anthropogenic disturbance—artificial fill over -10 Os Qsf1 Qca Qsi Qca Qs1 k k k k Olive-brown silty fine- to medium-grained sand; calcareous; carbonate in varying proportions; the surrounding diamict sediment of the New Ulm Formation, Heiberg Member sg 93°22'30" Qf1 Os 93°22'30" Qs1 Qca Qs2 k kk k k Ql Holocene lacustrine -10 Lake Henry Outwash Qh1 scs Qsx scs Rogers Rogers Qf2 j Os Qh2 Qtt k alternating beds of silty fine-grained sand and fine- to contains less shale where there are also sand seams—till of the Olive-brown to very dark gray loamy diamict; massive; soft; depth Sauk Centre SAND AND GRAVEL BODIES Qh2 j Qeo j Qf1 Qs3 Qs1 k -20 800 Qca Qs2 k k -20 Dark grayish-brown fine- to coarse-grained sand Qsh medium-grained loamy sand from 10'-22', massive fine- New Ulm Formation, Heiberg Member of oxidation fluctuates between 26'-34'; pebble-rich in the Qsf2 j j Qet Qml Qs2 Qca F k F' Qh2 Qsf2 Os j Qsc Qcl k k k and gravel; calcareous; fines downward to a silty -20 j Qcl 1 grained sand below; scattered gravel clasts increasing in Formation Qsf1 j kkk uppermost 30'; sandy seams at depths of 19', 41', 48', 60',103.5', Member s j Qsf1 Qs3 Qcs Qsf1 Qsf1 k kk k gt Qeo Qsf2 Qcs Qs2 k fine-grained sand; scattered cobbles above 48'; -30 abundance with depth; many shale and lignite sand grains— 108', and 111'; contains an average of 36% shale in the very Till Qsc sct Qxt sct 750 s s s Qh2 Qsf1 Qh2 k -20 tm s s k k -30 concentrated bands of shale and lignite where stagnation deposits of the New Ulm Formation, Heiberg coarse-grained sand fraction—till of the New Ulm Formation, 94 R. 21 W. 94 R. 21 W. s HPNDNR-1 ¦§ ¦§ s tm Qml j Qml Qh2 Qs3 Qs3 finer-grained; wood sampled at a depth of 58.5' Member -30 Heiberg Member tm Qsf2 Qml -40 Qht HENNEPIN WRIGHT ANOKA SHERBURNE CARVER SCOTT 700 tm k generated an infinite radiocarbon age (Table 2)— No core recovery, but section is most likely the same as the Qsf2 s Qml outwash of the New Ulm Formation, Twin Cities Elevation (feet above sea level) tm k -40 unit above and below (unit Qsh) Qet Qsf2 Qf2 -30 Qet s Qsf2 j Member -50 -40 650 tl tm s Approximate age present) Marine Isotope Geologic age (calibrated years before Speculated Qsr tm Stage (MIS) West East Outwash Qf1 fs1 R. 24 W. Qp Qp Qp R. 24 W. s Qts St. Francis Peat hp pe tm Qeo -50 sc Qp 1 -60 ¤169 600 ¤169 13,600 -40 -50 TILL AND FINE-GRAINED SEDIMENT tm Formation Ql hl Qll Ql Qm Ql tl Heiberg Member, Qht Till Qrt ft1 Lake sediment ¤ lb ¤ Twin Cities Very dark gray silty fine-grained sand; calcareous; inclusion Qsf1 -60 52 52 Figure 2. Diagram showing relative age, location (across Hennepin County -70 of diamict from 68'-69.5' interpreted as flow till; fines 550 tl Villard Member, Qtt from west to east), provenance (Plate 3, Fig. 2; Table 1), and related unit 14,150 Member downward to bedded silt and clay from 95'-102'; silty fine- -60 Alluvial fan sediment af Qf Qht Osseo 45°7'30" Osseo 45°7'30" labels from the cross sections for late Wisconsinan and pre-late Wisconsinan Qvt -80 grained sand from 102'-104'; coarsens to fine- to medium- -50 Automba -70 grained loamy sand from 104'-106', silt from 106'-108'; many 500 ? Dark gray silty fine-grained sand to silty clay; coarsens upward; Alluvium Qas glacial tills (Table 1). The age column and unit drawings are not to scale. All Qmt New Ulm phase Qsh shale and lignite grains throughout—stagnation deposits of 2-4 silt and clay is laminated in the lower 5.5' of the unit; silt laminae -70 Outwash Qh2 sx ha Qa Qa ss al Qa Al Each water-well record describes the vertical sequence of earth materials at the location of the REFERENCES radiocarbon ages shown are calibrated to calendar years before present (cal Formation -90 the New Ulm Formation, Heiberg Member Qvs are thicker than the clay laminae; streaks of dark gray and black mls Qsp mls T. 119 N. INTRODUCTION C T. 119 N. Moland Qca -80 Lake Henry Meyer Lake Holocene Qag C' 16,500 Very dark gray, complex mix of laminated silt and -60 are very small disseminated grains of shale and lignite— Qml Crow River Lake Rebecca Lake Sarah County Road 19 Peter Lake State Highway 55 County Road 101 Interstate 494 YBP; Stuiver and others, 2017). See the text on Plate 3 for a discussion of the Member ? sediment well. Glacial1,100 till is generally described as "clay" by well drillers, and although sand and gravel clay, sandy loam diamict, and loamy sand and -100 sand/lacustrine of the New Ulm Formation, Villard Member )252 )252 Late Wisconsinan 18,750 -80 gravel; calcareous; the upper 40' of this unit are Formation Member The Quaternary sand and gravel deposits of Minnesota are the products of a long, complex Knaeble, A.R., 2013, Quaternary stratigraphy, pl. 4 of Tipping, R.G., project manager, Geologic late Wisconsinan geologic history. The age of greater than 200,000 YBP for the St. Croix phase, Qcs Very dark gray loamy diamict; calcareous; contains an average Qml mlt mlt xt Qc co Qc can occur within a till, more extensive deposits tend to occur at the contact between two till layers. -90 composed primarily of laminated silt and clay; Till Qpt Qvs Colluvium ? Qvt of 7% more sand and 14% less shale than the above diamict; 1,050 pre-late Wisconsinan stratigraphy is based on a uranium series minimum age of dense; fines downward generally with a siltier layer -110 Very dark gray clay loam to sandy loam diamict; calcareous; glacial history that makes the subsurface mapping of these potential water-bearing units (aquifers) atlas of Wright County, Minnesota: Minnesota Geological Survey County Atlas C-30, 6 pls., Qvt -70 coarsens with depth; silty seam at 65.5'—till of the New Ulm Where two clay (till) layers related to different depositional events were not separated by a sand interglacial marl found atop a till unit stratigraphically above the Sauk Centre Emerald phase, Qce Cromwell Formation from 104.5'-107.5'; silt laminae may also contain top 1' of unit is a clay loam with abrupt transition to a sandy -90 93°45' Eolian sediment Qe Qe 93°45' -100 Formation, Villard Member Qe ss difficult. Establishing the location and characteristics of these sand and gravel units, however, is Qht scale 1:100,000. 32,550 coarse sand grains; laminae thickness varies Qts1 loam to 114'; visible carbonate and shale sand grains—till of Brooklyn 1,000 Brooklyn Mississippi Member of the Lake Henry Formation (Knaeble and Meyer, 2007; Johnson and -120 Brown fine- to coarse-grained sand and gravel; slightly layer, their contact was recognized by a change in the driller's description of the clay's texture (for throughout; clay laminae thicken with depth and the New Ulm Formation, Villard Member Pike Lake U.S. Highway 169 Shingle Creek Interstate 94 River >200,000 calcareous, more calcareous below 96'; coarsens upward; poorly Terrace sand Qat wmt Qt Qwl Qwr Qtl Qtu ssCenter tg tl tr Qts Qtg Qtl Qtr an essential step toward identifying aquifers and ensuring their appropriate use and protection. It is Qht CenterQvt Ql Ql Lusardi, B.A., 2009, Quaternary stratigraphy, pl. 4 of Bauer, E.J., project manager, Geologic atlas others, 2016). The Elmdale Formation in Hennepin County may correlate with silt laminae thin. The lower 60' are composed of Qcs Dark grayish-brown fine- to coarse-grained sand and gravel; -80 -100 Qf2 Maple example clay/sandy, clay/clay,Maple and gravel),Ql density, or color. In general, the moreQl detailed logs in Qht Ql State Highway 100 -110 sorted from 73'-89'; no gravel-sized grains below 89'; mostly fine- Outwash prs Qsv fs2 ) ) 950 Ql sandy loam, loamy sand and gravel, silt, and clay; -130 calcareous; coarsens slightly with depth; contains carbonate 55 55 the Pierce Formation mapped in Washington County (Meyer, 2016) and west- Sauk Centre Member to medium-grained sand from 89'-109'; wood sampled at a depth St. Francis Lake sediment also useful for mapping potential aggregate resources. In Hennepin County, this project employed Qvs Qcs Qvtof Carver County, Minnesota: MinnesotaQvt Geological Survey County Atlas C-21, 5 pls., scale soft; represents sediment within a stagnating block and red sand grains indicative of mixed provenance—sand Qlt Grove Qwf Qwc any particular area wereGrove given more weight by the geologist in drawing unit boundaries. Using the Qtt Qsc of 92' generated an infinite radiocarbon age (Table 2); fines to a beneath terrace sand Qs2 Qsc Qcs central Wisconsin (Baker and others, 1983; Syverson and others, 2011) based of ice—stagnation deposits of the New Ulm of the New Ulm Formation, Twin Cities Member 900 Ql Qht Qcs Qtt -120 -140 silty fine-grained sand from 111'-114'—outwash associated with -110 Formation 94 a process that combined the understanding and expertise of a geologist and a geologic information Ql Qf1 1:100,000. on its texture, lithologic composition, and stratigraphic position. The Pierce Formation, Twin Cities Member Very dark grayish-brown to brownish-gray loamy diamict; Till Qsf2 prt Qvt ft2 available data, contact lines were drawnQvt along each cross94 section, with each line representingQsf1 the Qs2 Qs2 St. Francis Formation, Qsf1 -90 the Cromwell Formation, St. Croix phase § Qmt Qs3 Qcs Qcs noncalcareous; contains many carbonate (17%) and red Dark grayish-brown silty fine-grained sand to medium- to coarse- ¦ ¦§ Ql Qs3 Qsf1 Qca Qas specialist with the data-handling capability of a geographic information system (GIS) to create Qs2 Qag Formation in Wisconsin has reversed polarity in the stratigraphically lower Qst Qs2 Sand and gravel Qnd Qbg Qbg base of a unit850 of sandQcs and gravelQsc or till. GISQf1 software was used to extract elevation values Qs3from ———2013, QuaternaryQcs stratigraphy, pl. 4 of Lusardi, B.A., project manager,Qat Geologic atlas of -150 Qh2 coarse sand grains indicating mixed provenance; interpreted -120 grained sand and gravel; fines upward overall; silty fine-grained T. 118 N. T. Qs2118 N. Qca -130 nbs Qsf1 Qsc members and normal polarity in the upper members (Syverson and others, 2011), to be Cromwell Formation mixed with the Lake Henry diamict inclusion at a depth of 126.5'; silty below inclusion but Qvt 494 three-dimensional models of Quaternary sand and gravel bodies. The distribution of sand and gravel Qf1494Qsf1 Qml Os Qh2 Qs3 Qcs Qts Qts Meyer Lake Member, Qml New Brighton vertices along each unit line and convert those into aQsf1 gridded surface by interpolatingQf2 the elevation Sherburne County, Minnesota: MinnesotaQs3 Geological Survey County AtlasQs2 C-32, 5 pls., scale Qst Formation, Sauk Centre Member—till of the Cromwell -100 coarsens below 130'; lithologic composition of the gravel grains Sand Qnb nls ¦§ Qbs Qbt Qbs 93°15' 800 ¦§ 93°15'j Qf2 Qs2 Qs2 which suggests that deposition occurred during the Brunhes normal-Matuyama 8 -160 Qf2 Qvs ¤Formation Qsf2 Qml Qsf2 -140 Formation, St. Croix phase indicates mixed provenance, but the very coarse-grained sand ¤ Os 12 New Hope at the land surface was mapped by the geologist from 12exposures, shallow auger holes, soil maps, Qf2 NewQh2 Hope Qml s Os Qtt -130 Unnamed Outwash Qwo pws R. 23 W. Qf2 Qsf2 R. 23 W. 1:100,000. Qsf2 Qcs reversed polarity boundary at 780,000 YBP (Lisiecki and Raymo, 2005). The through fraction indicates only slightly mixed provenance—sand of the New R. 24 W. data. The resulting rasterQsf2 data sets represent the distributionQf2 of the geologicQsf2R. units 24 overW. the county Qet Os Ops Ops Qs2 Dark olive-gray to light olive-brown with depth, fine- to Qbc j s j j Qeo Qsf2 Os Qet Os 20 St. Francis Formation, Qsf2 -170 Silt and clay landforms, and previous geologic maps (see Plate 3, Surficial Geology). In contrast, interpreting sand 750 Qvo Os tm Elmdale Formation in Minnesota does not show this same reversal; in fact, coarse-grained sand and gravel; organic material mixed with Ulm Formation,Villard Member Rainy Qet s s Qet Qs3 or in three dimensions. Till surfaces were iterativelyQeo modified untilQu thej geologist was confident that QetLusardi, B.A., andQet Tipping,Qeo R.G., 2006, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., project Os -150 the sand in the top 1' of the unit; sulfuric odor; coarsens with -110 Plymouth Plymouth Os Qu Os the majority of samples have normal polarity (Meyer, 1986). However, given greater -140 Independence distribution in the subsurface relied primarily on well records, scientificIndependence drill core, and drill cuttings j tm tm Qet Ops Ops Qet Ops depth; leached to a depth of 172' where it becomes very j Qvo Qvo j Os Pre-Wisconsinan -180 provenance Till Qwt pwt ¤ they adequately700 representedQot the stratigraphic interpretation forj the majority¤ of thetl water-well data j Opo Ops Very dark gray sandy loam diamict; calcareous; massive and 52 52 manager, Geologic atlas of Scott County, Minnesota: Minnesota Geological Survey County the variability in polarity found in Wisconsin, it is possible that the Elmdale calcareous; contains a large proportion of carbonate where Qu Ops ? W Sequence, Qwt Qml Very dark grayish-brown sandy loam diamict; calcareous; dense; contains more and larger cobbles than the diamict above; Elevation (feet above sea level) s j Qcs dz (see Plate 4, Quaternary Stratigraphy, Fig. 1 and cross sections for locations). Sand-distribution s Qu j Qu j -160 unleached; many weathered clasts of primarily felsic contains a significant amount of carbonate coarse sand grains Qvt Stagnation facies Ops Formation in Minnesota was deposited later during the same glacial event as the Qf2 very coarse-grained sand fraction indicates slightly mixed in the county. A similar process was followed for the surfaces of the sand and gravel bodies to Atlas C-17,s 6 pls., scale 1:100,000. -190 pebbles; lowermost 1' of unit contains large cobble of local -120 -150 650 s j but also numerous red coarse sand grains, which together provenance—till of the Villard member of the New Ulm Formation )100 35W models are based on the assessment of these data, consideration of the processes that deposited the )100 35W Opo Pierce Formation. The age of the reversal correlates it with the end of MIS 20. bedrock—outwash of the Lake Henry Formation, Meyer s indicate mixed provenance; carbonate content increases with nlc Qns Qnl ensure they conformed with till and water-well data. After both till and sand surface grids were Opo Opo Elmdale Formation, Qet Qcl Dark grayish-brown silty fine- to medium-grained sand; calcareous; Ice-walled lake sediment ¦§ § tlMeyer, G.N., 2013,s Quaternarys stratigraphy, pl. 4 of Setterholm, D.R., project manager, Geologic -170 Lake Member depth from 7-15%; subtle color change from reddish to dark ¦ -200 ns Qs2 coarsens upward; upper 2' contain a small amount of very coarse- Outwash Qeo pws 94 glacial sediment, and an understanding of the glacial history in the county. Despite basing these 600 94 1 Olive-gray loamy diamict; calcareous; contains gravelly grayish-brown also indicates mixing; interpreted to be Cromwell -160 S3 ¦§ complete, they were processed through GIS raster calculations to ¦§create a set of top and bottom Ages are in calibrated/calendar years before present (cal YBP), and Qcs grained sand indicating Superior provenance—lacustrine of the Elmdale Glacial Lake ) Qng 45° 45° atlas of Anoka County, Minnesota: Minnesota Geological Survey County Atlas C-27, 6 pls., seams; abundant carbonate—till of the Lake Henry ) Formation with material incorporated from the Sauk Centre 55 models and interpretations on the best available data, they are incomplete in some areas because of 55 V sequence, Qot -130 Qh1 Cromwell Formation Grantsburg sediment recalibrated from published radiocarbon dates using CALIB radiocarbon calibration -180 -210 Formation, Meyer Lake Member Member of the Lake Henry Formation—till of the Cromwell T. 29 N. surfaces and550 a thickness for each geologic unit. The result is a three-dimensional geologic modelT. 29 N. Very dark gray sandy loam diamict; calcareous; Brown medium- to coarse-grained sand and gravel; slightly Formation Minneapolis Minneapolis scale 1:100,000. Formation, St. Croix phase -170 Till Qet pwt a lack of data. As a result, unit extent, thickness, stratigraphic correlation, and even the material program, Calib 7.1 (Stuiver and others, 2017) with 2 sigma error. dense, deposited subglacially; common carbonate Light olive-brown loamy sandy gravel; contains slightly less calcareous; concentration of gravel/cobbles marking the contact Qpc T3 Light olive-brown fine- to coarse-grained sand and gravel; Qs3 Outwash of tills and sands for the county. Qtt and red pebbles; large lignite clast at 182'—till of -220 carbonate and more red grains than above; sharp contact with the underlying unit interpreted to be an erosional lag—outwash 394 Qno ng nhs sd Qdo S1 394 500 EXPLANATION -190 -140 leached to a depth of 126', calcareous below; contains Plymouth of buried units may not be as well constrained as for the surficial units. Plymouth the New Ulm Formation,Twin Cities Member with underlying bedrock—outwash of the lower St. Francis associated with the Cromwell Formation, St. Croix phase ¦§ ¦§ Riding Mountain-provenance Formation decomposed cobbles of primarily felsic lithologies; generally -180 The geologic model should be considered a guideline for the occurrence and approximate Winnipeg-provenance -230 Brown sandy loam diamict; slightly calcareous; massive and Lacustrine Orono Orono deposits more gravelly with depth; abundant carbonate where Qhl dl The unconsolidated Quaternary sediments that overlie the bedrock in Hennepin County are highly deposits Light gray to white, well-rounded, well-sorted, fine- to pebbly; very coarse-grained sand fraction indicates Superior D -200 Brown medium- to coarse-grained sand and gravel; unleached—outwash of the Lake Henry Formation, Sauk Centre thickness of major sand bodies. The model does not guarantee sand and gravel will be found at all D' Rainy-provenance medium-grained, quartzose sandstone with some interbeds provenance; contains 6% carbonate on average—till of the Unnamed Wayzata 1,100 Period of sediment erosion calcareous; silty fine-grained sand lens from 217'- -240 -150 Member Outwash Qvo sdi variable in character and thickness. These deposits are largely the result of numerous, distinct ice Wayzata County Road 19 Interstate 394 Long Lake Hadley Lake Gleason Lake Interstate 494 deposits of gray and greenish-gray shale—Middle Ordovician, St. -190 Cromwell Formation,St. Croix phase Ice-contact Qhi and/or deposition of 220'; extra cobbly and gravelly roughly every 5'; Yellowish-brown fine- to coarse-grained sand and gravel; Heiberg places shown, nor does it preclude them being found where they are not shown. It does indicate Superior-provenance Peter Sandstone Superior nonglacial sediment -210 bottom 4' are a gravel/cobble mix of glacially- calcareous; contains decomposing cobbles of primarily felsic Brown to dark grayish-brown fine- to coarse-grained sand and Member 394 advances during the Pleistocene Epoch (see Plate 3 and Plate 4, Fig. 2). Most of the aquifers within 1,050 394 deposits -250 Cream, red, and gray shale; some intervals blocky; lower 20 Qts, Qts2, Qti Stagnation Qsh ¤169 where sand features with large areal¤169 extent and significant thickness are likely to be encountered. derived and local bedrock—outwash associated lithologies; generally more gravelly with depth; contains slightly gravel; slightly calcareous; grain size alternates from finer to St. Louis St. Louis cm are weathered-looking purple, brown, red, and gray silty Qh2 ¦§ ¦§ -200 coarser; generally more well-sorted with depth—outwash provenance Qot with the Cromwell Formation, St. Croix phase -160 more carbonate than the above unit; also more oxidized than Till the Quaternary section consist of sand and gravel deposited by proglacial or subglacial meltwater. -220 shale Park Where data1,000 are limited, for example where wells Parkend in a Quaternary sandQsh and gravel unit, geologic Qsh Qts -260 Os above—outwash of the Lake Henry Formation, Meyer Lake Qf2 associated with the Cromwell Formation, Emerald phase Till Qht ht hbt htw dtc dth Qd Qds Qdc T1 State Highway 55 U.S. Highway169 State Highway 100 Bassett Creek Interstate 94 Mississippi Nicollet Island Interstate 35W Qs2 Gray-brown, well-rounded, well-sorted, coarse-grained, Layers of unsorted sediment composed of clay to boulder-sized particles (diamict) interpreted to Qht quartzose sandstone with iron-coated grains fining-upward Member Dark yellowish-brown to olive-brown fine- to medium-grained sand; interpretations relating to the extent of sand and gravel bodies and their thickness tend to depict less Qht Qsh Qts River -210 Qvs Qht to gray-cream shale interbedded with coarse-grained, rare gravel; noncalcareous; generally massive with some bedding Qvs nts sdv 950 Qtt Qvt Qvt Qvt -230 -270 Villard Sand have been deposited directly by glacial ice (till), as well as fine-grained, bedded sediment deposited Ql CONTOURS FOR FIGURES DEPTH FOR FIGURES Table 1. Average values for the matrix texture and composition of select tills recognized in Hennepin quartzose sandstone and pebbles fining-upward to cream- -170 from 206'-208'; contains decomposing cobbles of primarily felsic ) material than may actuallyQvs be present. Qs2 Additionally,Ql erosion by ice and meltwater duringQtt Qvs subsequent) Qtt Qtt lithologies—outwash of the lower St. Francis Formation Undifferentiated sand Qsu psu suu su New Ulm Member Minnetonka 55 MinnetonkaQl 55 Ql County. Matrix texture (the less than 2 millimeter grain-size fraction of the sample) is expressed as gray and purple-red shale Qvt vtw into ponded proglacial meltwater, form low permeability confining layers (aquitards) that enclose the Qs2 -280 -220 Till vt nt Qnt Qna dtv Qdl T1 900 Qmt Qcs Qs2 3Qs2 THROUGH 15 5 THROUGH 15 -240 Brown, well-rounded, well-sorted, medium- to coarse- Brown, white, and tan, well-rounded, well-sorted, fine- to coarse- Formation glacial events may have removed portions of older sand bodies. Where incomplete data did not Qsh Qcs Ql relative proportions of sand, silt, and clay in percent. The lithologic composition of the very coarse- Qvt Qcs Qtt Qvt Qtt grained, quartzose sandstone interbedded with gray and red grained, quartzose sandstone; oxidized in upper 1'—Late 35W aquifers. The till layers left behind by each ice advance tend to be laterally continuous because glacial Qtt Qtt 35W Qcs Qcs Qcs Qs2 Qts Qtt -180 Cream-yellow, well-rounded, well-sorted, very fine- to fine-grained, Outwash Qts allow for stratigraphic interpretation, sedimentsQs2 were categorized as PleistoceneQcs undifferentiated Qs3 Qs2 Qat grained sand fraction (1-2 millimeters) is expressed in percent as relative proportions of Precambrian shale, iron-cemented sandstone, and siderite Cambrian, Jordan Sandstone ¦§ 850 Qs2 ¦§ Thickness of a geologicOpg 0–50 Qtt -290 j shaley, quartzose sandstone and gray shale in upper 2' to yellow, Qsc Qsc Qsc Qvt Qcs Ql -230 tco ) Qce) Qs3 Qs3 Qs3 Qcs Qcs Qag -250 Brown and gray-white, well-rounded, well-sorted, medium- well-rounded, well-sorted, fine-grained, quartzose sandstone—Late Qu pu ups ups St. Bonifacius 7 Qsl Qno ns S2 ice usually covered the entire county. GlacialSt. meltwater Bonifacius is capable of producing large, extensive 7 Qsc Qf1 Qsf1 Qsc Os Opg Qcs Qtt crystalline rocks, Paleozoic carbonate rocks, and Cretaceous shale using the classification system Ops Red-pink and gray dolostone and sandy dolostone Undifferentiated Qu Un deposits (unit ). This includes sand bodies (unit ) that could not be assigned to a specific unit contouredQsc at 20 foot (6 Opg Opg Qat Od to coarse-grained, quartzose sandstone Sand Qts2 Qu Qf1 Qsu Qs3 Qh2 Qsf1 Qs2 Qf1 Qs3 Qts Opg with small vugs—Late Ordovician, Prairie Du Chien -300 tm Cambrian, Mazomanie Formation,Tunnel City Group Qtt, Qst deposits like outwash plains, but it can also generate more localized deposits in channels or basins 800 Os Qh2 Qsf1 Opg Qs2 Qlt of Hobbs (1998). The Precambrian crystalline 1-2 millimeter fraction is further differentiated by Green-gray and dark red, fine- to medium-grained, shaly Excelsior T. 28 N. Excelsior Qsf1 Qf1 Os T. 28 N. Qf2 Os Qsf1 Qs2 Opg Opg Od Group, Shakopee Formation -190 glacial advance. In general, at increasing depths in the stratigraphic section, data availabilityOps meter) intervals. Os 51–100 Os Opg Opg sandstone and very sandy shale with iron-cemented -240 Bedrock Topography ) Qh2 Qsf1 Qml tl Os Os Qts crystalline rock type: light (felsic rock types including granite, gneiss, and other light-colored Fe Brown, orange, gray, and green, fine-grained, shaley, quartzose Qtc ) Qs2 Fe 7 Colluvium Edina at the lower elevations of the landscape. In addition,7 glacial meltwater is capable of depositing Edina Qml Qml Os Opg Qst Opg Os -310 sandstone layers; ooidal chert with pyrite (possible Prairie Figure 5. Descriptive log of rotary-sonic core HS-3 drilled by Traut 750 Qml Ops Ops Os metamorphic rock types), dark (mafic rock types including basalt, gabbro, diabase, and also dark- Figure 3. Descriptive log of rotary-sonic core HS-1 sandstone with heavy oxidation and liesengang; rare glauconite 494 diminishes and delineated494 units could be more or less discontinuous than shown. Any west to east du Chien Group intraclasts) at 308' and 310.5' Basal sand and gravel zus Qml Os Qf2 Qf2 Ops 20 Depth in feet fromOs theQs3 land Companies for this study. Drill-site location is shown on Figure 1 near base Lacustrine Qtl § sand and gravel during both the advance and the retreat of a glacier within one glaciation. As a Os Os colored metamorphic rock types), and red (iron formation, rhyolite, agate, and sandstone). drilled by Traut Companies for this study. Drill-site -250 ¦ § Qf2 Os ¦ Os 101–150 patterns on Figures 5j through 16j are an unavoidablej artifact of cross-sectionj creation and digital Ops Os Qcs -320 and Plate 1. Unit symbols and colors match those shown on the cross Gray very fine- to fine-grained quartzose sandstone and green Twin Cities 700 Qu Qsf2 Qsf2 Ops Os surface to the top of a sand tl result, glacial till from an ice advance may bury sand and gravel associated with the same advance tl 40 Qu location is shown on Figure 1 and Plate 1. Unit symbols shale with abundant glauconite; well-cemented sandstone and
) Elevation (feet above sea level) ) Qu 62 62 Opo Opo Os sections. See Table 1 for matrix texture and composition averages Member Stagnation Qst processing. Despite these limitations, the geologic model provides a realistic interpretation of Opo Qs3 MATRIX TEXTURE CLAST TYPE siltstone with pink dolomite grains from 252' to bottom—Late )77 s Qeo )77 and colors match those shown on the cross sections. See -330 and/or sediment deposited during a previous glacial event. At the same time, a glacier is capable of 650 60 and gravel unitOps (depth from Gray, well-rounded, well-sorted, medium- to coarse-grained, of till units. Quaternary sediment in this core is late Wisconsinan -260 Cambrian, Lone Rock Formation,Tunnel City Group 44°52'30" )100 44°52'30" 100w Qet 151–200 Percentage of total grains tm ) Ice-contact where and what kind of geologic units lie inw the subsurface of Hennepin County. However, given Qet Ops Table 1 for matrix texture and composition averages of j quartzose sandstone—Late Cambrian, Jordan Sandstone Figure 2. Correlation diagram showing the stratigraphic position of all units in Hennepin County compared with equivalent units mapped in Wright (Knaeble, 2013), Anoka Qti )5 Qni Qdi )5 j the land surface to the top of Ops Qu Ops counted of the 1-2 in age to a depth of 119 feet (36 meters). Richfield deforming, eroding, and incorporating the underlying substrate. The net result of each glaciation, Qet Richfield 80 Percentage of total till units. All of the Quaternary sediments in this core are -340 Figure 6. Descriptive log of rotary-sonic core HS-4 drilled by Traut the limitations600 of the data, the model should be used as a guide and should not preclude further millimeter fraction Figure 1. Selected stacked surfaces from the land surface to the bedrock surface. Representative major sand bodies underlying Hennepin County are on the left, with the intervening till and fine-grained j undifferentiated sediment is Percentage of the crystalline grains Companies for this study. Drill-site location is shown on Figure 1 Till Qtt tct nt Qnd Qnt Qnc nt Qdt T2 given all of these factors, is a highly disturbed, discontinuous stratigraphy with complex cross-cutting e 100 201–250 late Wisconsinan in age. A small inclusion of Cromwell Figure 4. Descriptive log of rotary-sonic core HS-2 drilled by (Meyer, 2013), Sherburne (Lusardi, 2013), Carver (Lusardi, 2009), and Scott (Lusardi and Tipping, 2006) Counties. Unit in Wright County is described on the Surficial site-specific investigations or inspection of individual well logs. s s Opo less than 2 millimeter counted and Plate 1. Unit symbols and colors match those shown on the cross cg Eden 550 Eden j Opo fraction Formation sediment is present at the base of the Twin Traut Companies for this study. Drill-site location is shown Qts1 relationships (Fig. 1). By convention, the depicted sand and gravel bodies are named after the till 120 shown on Figure 15). sediment layers on the right. Reddish areas are where the surface of each unit is at higher elevations (lighter gray for the bedrock surface), and greenish areas are where each unit is at lower elevations Sand below till Prairie Prairie Cities Member till in this core, and it contained 7 percent on Figure 1 and Plate 1. Unit symbols and colors match those sections. See Table 1 for matrix texture and composition averages of till Geology plate as an ice-contact unit but as outwash on the Quaternary Stratigraphy plate, so it is correlated with both the ice-contact (unit ) and outwash (unit ) units in Quaternary deposits in Hennepin County are listed in stratigraphic order along with equivalent j Qsi Qs2 494 underlying them, but exceptions were made for those at the land surface, above undifferentiated 500 494 140 251–300 carbonate and no shale in the 1-2 millimeter very coarse- shown on the cross sections. See Table 1 for matrix texture units. Quaternary sediment in this core is late Wisconsinan in age to a Total number Total of samples Gravel (percentage of total sample weight) Sand Silt Clay Precambrian crystalline Paleozoic carbonate Light Dark Red (darker gray/black for the bedrock surface). Units are superimposed onto the bedrock surface to emphasize their preferential preservation in bedrock depressions. ¦§ units from adjacent Wright (Knaeble, 2013), Anoka (Meyer,§ 2013), Sherburne (Lusardi, 2013), Deposit description Cretaceous shale depth of 185 feet (56 meters). A 2-foot (0.6-meter) section of Cromwell 212 ¦ Qms ¤ ¤212 160 grained sand fraction. and composition averages of till units. Quaternary sediment Sand ms sediment, and where data were sufficient to make that determination. Hennepin County. Unit Qwl in Anoka County includes units Qwn, Qwi, and Qwt, and unit Qwr includes unit Qwd. The pre-late Wisconsinan Quaternary stratigraphy for Scott Moland Carver (Lusardi,E 2009), and Scott (Lusardi and Tipping, 2006) Counties in Figure 2. The more E' New Ulm Formation Formation sediment was cored at this site, and it contained an average 301–350 Heiberg Member (unit Qht) 591 5 42 38 20 40 26 34 88 11 1 in this core is late Wisconsinan in age to a depth of 123 feet Member Qmt In order to model this stratigraphy, 103 cross-section lines spaced 0.3 mile (0.5 kilometer) County Road 92 Whaletail Lake Langdon Lake Black Lake Lake Minnetonka County Road 101180 Interstate 494 State Highway 7 U.S. Highway169 Minnehaha Creek State Highway 100 of 6 percent carbonate in the 1-2 millimeter very coarse-grained sand Till mt Qdd T1 extensive1,050 sands portrayed by the geologic model are shown in Figures 3 through 15, ranging from Villard Member (unit Qvt) 268 7 48 35 17 56 25 19 86 12 2 (37.5 meters) and pre-late Wisconsinan in age to 190 feet (58 County was not differentiated to the same extent as other atlases. Unit Qpc in Scott County is the Pierce Formation, which may correlate with the Elmdale Formation (see Plate Bloomington Bloomington 200 Moland Member (unit Qmt) 18 10 62 27 11 69 26 5 83 15 2 meters). A thick interval of bedrock was cored at this site to fraction, which is also the average amount for the county. A thicker ¤169 35W apart were generated in a west–east direction (Plate 4, Fig. 1). The results from the cross-section 169 35W Mississippi T. 27 N. ¤ Twin Cities Member (unit Qtt) 133 7 55 30 15 72 18 10 73 18 9 the youngest1,000 sands at the land surface to buried, progressively older sands (Fig. 1). A numberT. 27 N.of Qtt 351–400 sequence of bedrock was cored at this site to determine the elevation Qs2 ¦§ ¦§ 220 and greater HS-1, 277941 Interstate 35W State Highway 55 River examine the nature of the unconformable contact between the 4, Fig. 2). The subsurface extent of unit shown on Plate 4 of the Scott County Geologic atlas may include other Winnipeg-provenance units such as the Sauk Centre and Meyer analysis are available digitally as raster data sets for the top and bottom elevation surfaces and Cromwell Formation (unit Qcs) 129 11 62 27 11 94 6 0 54 28 18 of the contact between the Mazomanie and Lone Rock Formations of T3 Ice-contact Qsi cg Qci Qci csr Qci factors determine whether or not the sand and gravel units depicted here are usable aquifers. To be Ql Qts St. Peter Sandstone and the Jordan Sandstone in the absence of 950 Lake Henry Formation thickness of each interpreted unit of till and sand. Examples of these interpretations along six of Qht Qht Note: Contour lines may not close at the Prairie du Chien Group (see Plate 2, Bedrock Geology, for the Tunnel City Group (see Plate 2 for more information). Qs1 csa an aquifer, the units must be saturatedQl and able to readily transmit water to a well. Their capacities Ql Qsi Qsh Qtt Qag Sauk Centre Member (unit Qsc) 44 6 36 42 22 56 44 0 86 12 2 Lake Members of the Lake Henry Formation. Some units shown in the diagram are not shown on the printed cross sections but appear in the digital files of other cross sections. Outwash Qhi Qsh Qsi Meyer Lake Member (unit Qml) 41 5 39 41 20 67 33 t 82 15 3 these lines are shown in cross sections A–A' to F–F' on Plate 4. Along these lines, descriptions 900 Ql Qsh Ql Ql the edges of mapped areas. This is more information). for water storage and transmission depend on Qvttheir extent and thickness,Ql as well as factors such Qts Qcs Automba Qcs Ql Qcs Qts St. Francis Formation Till Qca an artifact of the digitalQsi processing.Qcs Qs3 Qtt Ql Qtt phase and samples from a combination of water-well records, rotary-sonic core, engineering test holes, Qvt Ql Qsh Upper Member (unit Qsf1) 12 10 62 26 12 89 11 0 71 17 12 Qlc cta as sediment850 coarseness, Qs2degree of sorting, consolidation, and potentialQs3 for recharge. Connectivity Qs3 Qml Qcs Qs2 Qs2 Ql leached 10 4 71 20 9 100 0 0 62 23 15 Lacustrine scientific cutting sets, and auger borings (Plate 1, Data-Base Map) were used to identify contacts Qsi Opg Qf2 Qag Qcl Qcs Qs2 Qml Qcs Qcs Lower Member (unit Qsf2) 4 3 59 26 15 90 10 0 83 13 4 INDEPENDENCE Cromwell between the sand and gravel units is alsoQs3 important. In many places, two or more sand and gravel Qsh SCALEOpg 1:300 000 Qat Surface East Qs2 Opg Opg leached 4 8 65 25 10 100 0 0 76 15 9 West CORCORAN 800 Qts Qts Qcs elevation West East Figure 3.Formation Fine-grained sediment at or near the surface—Model-generatedQco Qsc map showing the extent and between units in the subsurface. The geologistFigure provided 4. an interpretationSurficial of sand materials and that occurgravel —Model-generated map showing the extentOpo and thicknessQs2 of sand and Qvt Qf2 Os Surface Outwash Qs2 cg Qco csr units mayFigure connect 6.3 to — form Presence a single aquifer and Thicknessif there is no ofinterveningQce Sand and till layer. Gravel Water quality also 5 0 5 10 MILES Opg Od Rainy provenance (unit Qwt) 1 4 66 24 10 90 10 0 80 16 4 (feet) St. Croix Qs3 Qu Opg I-1007 elevation C-1001 Qcs in the areas between data points or at depths not penetrated by drill holes based primarily on an Qh2 Qh2 Os Opg Os Opg phase 750 Qcs Qcs Os Elmdale Formation (unit Qet) 2 4 53 31 16 83 13 4* 82 13 5 1,000 I-1001 Depth 242265 (feet) Depth 242222 thickness of surficial fine-grainedTill sedimentQcs (unitsct , , Qcr, , ,Qct Qcd, andctr [and unit where it gravel bodies generally occurring at or neardetermines the land whether surface.Qml an aquifer isIncludes suitable as unitsa source of drinking, ,water. , The maps, and ,reports , , Qml 242259 Ql Qc Qhl Qsh Qtc Qtl Qst Qp Sand in a terrace position at the surface asQas mappedQag (Qat)Qat andQnd contouredQnbOs totalQno thicknessQh2 Qts (Berthold and Lively, 2018). 5 0 5 10 KILOMETERS Qs2 Depth I-1014 (feet) Lithology I-1002 1,035 (feet) Lithology understanding of geologic processes. Qml Os Qml Qs3 Total 1,257 Lithology 242260 I-1009 0 produced by the Minnesotaw Department of Natural Resources,j as Part B of this County GeologicQml Qst INDEX FOR FIGURES 7 THROUGH 10 (feet) Depth 242272 0 Depth 700 Os Depth 242267 Emerald Outwash Qs3 cg1 Qse cse sr Qsf2 tl Qf2 Ops Os t = trace amount (less than 0.5 percent) 0 (feet) Lithology (feet) Lithology C-1006 overlies them] from Plate 3, Surficial Geology) occurring at the land surface or below surface water. Also , , , and the artificial fill associated with units , , and from Plate 3. Qf2 Qml Os (feet) Lithology Qhi Qti Qsi Ql Qti Qsi Qf2 Os Qtt Os New Ulm Formation—Moland, Villard, and Heiberg Members 990 0 0 Depth 242227 phase Atlas, take these and other factors into considerationQu to characterize hydrogeologic conditions. Ops Ops *includes Cretaceous limestone 0 1,030 -10 Elevation (feet above sea level) -10 s Ops Qcs (feet) Lithology Till Qce ct1 Qce cte rt 650 w Opo Os -10 Qu tm Qs2 0 includes unit , which occurs just beneath surficial units and/or the artificial fill associated with unit . Qu Opo Qu Opo Ops Os New Ulm Formation—Twin Cities Member -10 -10 Qlt Qat Ql e Os -20 -10 C-1004 -20 600 -20 1,025 242225 Cromwell Formation—Emerald, St. Croix, and Automba phases 980 Depth -10 Ops Qu Ops -20 -20 (feet) Lithology Outwash hs Table 2. Wood and charcoal were sampled for radiocarbon dating from five rotary-sonic cores and one -20 Hewitt 550 j j -30 0 -30 giddings soil auger boring. Three of the rotary-sonic cores (OB 27075; SF-1 and SF-2 from Carver County Lake Henry Formation—Sauk Centre Member -30 Formation 93°30' 93°30' -30 -30 1,020 -20 Till hwt Opo 500 to the southwest) were contracted by the Minnesota Department of Natural Resources and collected by St. Francis Formation—upper member -40 -30 -10 -40 the Minnesota Geological Survey. The other two rotary-sonic cores (HS-1, HS-3) were contracted and -40 R. 22 W. R. 22 W. -40 -40 -30 R. 23 W. R. 23 W. Lake Henry Formation—Meyer Lake Member -40 1,015 collected by the Minnesota Geological Survey. The samples were taken at the Minnesota Geological -50 -20 -50 Outwash sb F F' -50 Browerville Minnesota 93°37'30" 1,000 Rice Marsh U.S.Highway 212 Purgatory Creek New Anderson Lake U.S. Highway 169 Haeg Park Lake Interstate 35W 93°37'30"State Highway 77 Survey, prepared by LacCore of the University of Minnesota, and processed by the Center for Accelerator St. Francis Formation—lower member -50 -50 -40 Formation )101 Lake )101 River -60 -50 Till bt Mass Spectrometry of the Lawrence Livermore National Laboratory. All samples were in stratigraphic -60 93°30' 93°30' 93°30' 93°30' 93°30' T. 120 N. 93°30' T. 120 N. -60 1,010 -30 950 CROSS-SECTION SYMBOLS positions indicating they had the potential to yield finite age dates within the late Wisconsinan glaciation. Unnamed Rainy-provenance formation -60 -60 -50 -70 -60 C-1011 Qtc Most of these results indicate, however, that the ages of the organic materials sampled are older than the -40 -70 Elmdale Formation -70 1,005 Depth 242235 Lake Henry Outwash Qh1 scs Qsx scs sg Rogers 93°22'30"900 Qti Rogers 93°22'30"Geologic contact—Approximate. No-line boundaries occur where data were insufficient to reliably extend Sauk Centre reliable limit of radiocarbon dating because they are beyond the standard range of calibration curves used -70 -70 -60 (feet) Lithology Qh2 -80 -70 R. 23 W. R. 22 W. R. 23 W. R. 22 W. R. 23 W. R. 22 W. R. 23 W. R. 22 W. Formation R. 23 W. R. 22 W. R. 23 W. Qht R.Qts 22 W. Qti units. Unnamed Superior-provenance formation -80 0 Member Qsc Qxt sct gt Ql Qvt to calibrate radiocarbon ages to calendar years before present (Walker, 2005; Reimer, 2012). The one -80 -50 Till sct 94 850 94 ¦§ R. 21 W. Qat ¦§ SampledR. 21 drill W. hole—Includes cored rotary-sonic drill holes, archived split-spoon core holes, and cuttings sets sample with a finite age (QHPN-1) was generated from charcoal picked from lake sediment just above -80 -80 1,000 -70 Qtl -80 Ql Qts1 Qtl Qtt Ql Undifferentiated older sand and lake sediment mix -90 93°37'30" 93°37'30" 93°37'30" Qtl Qat from drill holes. Well cuttings may not have been collected from throughout the entire thickness -90 -60 -90 -10 93°37'30" 93°37'30" 93°37'30" Ql Qtc its contact with till from core collected in Rice Lake in Maple Grove. This age result is younger than 800 Qts -90 -90 -80 101 )101 Outwash Qf1 Qsr fs1 R. 24 W. 101 Qs2 R. 24 W. of the material drilled. The rotary-sonic hole is labeled with its assigned name. other nearby ages for the timing of deglaciation (Meyer, 1998), and only serves to constrain the onset -90 101 101 ) -100 ) ) 101 Qts2 ) St. Francis ) Qs2 T. 120 N. T. 120 N. Qti -100 -20 T. 120 N. T. 120 N. T. 120 N. T. 120 N. ¤169 ¤ 169 Drill hole—Includes water-well drillers' sites. The top of the drill-hole symbol may not coincide with the cross- of lacustrine sedimentation at that particular location in the lake. Peat/organic material -100 -70 Formation Till Qsf1 Qrt ft1 ¤52 750 Qtt Qvt ¤ -100 -100 Qc52 -100 -90 Qtt section surface-elevation line because the point is located near (within 0.15 mile [0.25 kilometer]) -110 Qcs Qcl Ql 13 14 14 Glacial till -110 -80 -110 -30 Osseo 700 45°7'30" Osseo 45°7'30" CAMS Sample name MGS ID Depth δ C Fraction ± D C ± C age ± Median Qcs but not on the cross-section line and therefore may have a slightly different surface elevation. number (feet) modern probability age -110 -110 Ops -100 sx Qml Os Qs2 Ice-contact loamy sand and gravel -120 -110 93°22'30" 93°22'30" 93°22'30" Rogers 93°22'30" Outwash Qh2 mls Qsp mls 93°22'30" T. 119 N. 93°22'30" Os Qas Bedrock contact—ContactT. 119 N. point shown at the base of the Quaternary deposits with the associated bedrock -120 -40 Rogers Rogers Rogers Qml Lake Henry Meyer Lake Rogers Rogers Ops 176552 SF-1-101 817606 101 -25 0.0002 0.0004 -999.8 0.4 >55200 N/A -90 -120 650 Qs3 -120 -120 Elevation (feet above sea level) )252 Ops Ops Qs3 map) 25unit2 label between contact points from Plate 2, Bedrock Geology. 176553 OB 27075-1-149.5 819504 149.5 -25 0.0015 0.0004 -998.5 0.4 52400 2300 N/A Formation Member Qs3 Sand and gravel -120 -110 Till Qml mlt Qpt mlt xt 176554 SF-2-215 817603 215 -25 0.0000 0.0004 -1000.0 0.4 >56900 N/A -130 Qcs Qml Qs2 Fault—Bedrock fault, see Plate 2. -130 -50 600 Opo Ops Qs3 176555 HS-1-58.5 277941 58.5 -25 0.0010 0.0004 -999.0 0.4 55200 3300 N/A -100 -130 93°45' Opo93°45'Qh2 Fine-grained sand -130 -130 94 94 94 94 94 94 Brooklyn Opo Brooklyn 176556 HS-3-92 277943 92 -25 0.0000 0.0004 -1000.3 0.4 >56900 N/A -140 -130 -120 R. 21 W. R. 21 W. R. 21 W. § R. 21 W. R. 21 W. Opo Opo ¦ Opo ¦§ ¦§ Qh2 -140 ¦§ ¦§ Center Center 176557 MDT-1-14 42945 14 -25 0.0013 0.0004 -998.7 0.4 53600 2700 N/A -60 ¦§ -140 Outwash Qf2 prs Qsv fs2 Maple 550 Opo Maple -110 St. Francis )55 )55 179057 QHPN-1 47009 15.5 -25 0.5057 0.0023 -494.3 2.3 5480 40 6284 -140 -140 Grove Grove -140 -130 -150 Formation 94 j j j 94 -150 Till Qsf2 prt Qvt ft2 ¦§500 ¦§ -120 -150 -70 Vertical exaggeration = 50x -150 -150 R. 24 W. R. 24 W. R. 24 W. R. 24 W. R. 24 W. R. 24 W. T. 118 N. T. 118 N. -160 -150 -140 494 494 -160 R. 21 W. ¦§ 93°15' ¦§ 93°15' -160 -80 169 169 169 ¤169 169 ¤12 New Hope ¤169 ¤12 New Hope -160 -160 -130 ¤ Unnamed ¤ pws ¤ Outwash Qwo R. 23 W. R. 23 W. ¤ R. 24 W. R. 24 W. Figure 6.4 — Representative Cross Section -160 ¤ ¤52 ¤ Silt loam to silty fine-grained sand (subsurface unit)—Reddish-brown other parts of the state. The position of the Elmdale Formation directly -170 -150 52 ¤ ¤ Rainy ¤ 52 Sand and gravelly sand (Surficial Geology unit)—Coarse-grained alluvium. Silty clay to silt loam (Surficial Geology unit)—Lacustrine deposits. Qcl the lower part of the unit locally contains more red Precambrian clasts 52 52 52 Plymouth INTRODUCTION Qag Plymouth Qtl -170 Independence Independence -140 -170 -90 provenance Till Qwt pwt ¤52 ¤52 (5YR 5/4) to yellowish-brown (10YR 5/4), silty, fine-grained sand to silt and silt than the upper part. The differences within the unit are the result on bedrock across much of the county suggests that this sandier texture -170 -170 Osseo 45°7'30" A portionThe Quaternary of cross Stratigraphy section plate shows F-F’ thefrom unconsolidated Plate 4, materials Hennepin expected County to Atlas (Berthold, 2018) shows the stratigraphy may be the result of incorporation of Cambrian sandstone. Given that -180 -170 -160 Osseo 45°7'30" Osseo 45°7'30" Osseo 45°7'30" Osseo 45°7'30" Osseo 45°7'30" Qc Loamy sand and gravel (Surficial Geology unit)—Colluvium. Qst Silty clay loam to sandy loam (Surficial Geology unit)—Stagnation deposits. loam deposited by meltwater of the Superior lobe between the Automba of erosion and incorporation of underlying Superior-provenance sediment -180 )100 35W )100 35W -180 -100 inbe encounteredthe area between of large the land landslides surface§ and bedrock along surface the in Minnesota Hennepin County. River Cross in Bloomington in the eastern portion of the section. Unit Qcl and St. Croix phases. The thickest deposits of this unit occur along the this unit is typically described in well logs as "blue clay," however, it -180 -180 -150 Bedrock ¦ ¦§ and interglacial lacustrine deposits (Table 1). This unit may correlate -180 Outwash Qeo pws S3 sections A–A' through¦§94 F–F' are representative of 103 cross sections (Fig. 1) spaced 0.3 PLEISTOCENE ¦§94 -190 -170 Bedrock Elmdale )55 45° Silty)55 clay to loamy sand and gravel (Surficial Geology unit)—45° Artificial Minnesota River from Eden Prairie east to Bloomington, just south of with the uppermost member of the informal Good Thunder formation may be finer-grained in many places in the county. Till. -190 T. 119 N. T. 119 N. T. 119 N. T. 119 N. T. 119 N. T. 119 N. Qti -110 Formation appearsmile (0.5Minneapolis kilometer) to be apartinvolved that were in constructed destabilizingT. 29 N. to create athe three-dimensional slope. model Minneapolis T. 29 N. the Minneapolis–St. Paul International Airport (cross section F–F'). The -190 -190 -160 Till Qet pwt Qpc T3 Late Wisconsinan fill associated with this unit is shown with a stippled pattern. Ice-contact identified in south-central Minnesota (Johnson and others, 2016). Till. Unnamed formation of Superior provenance—Sediment of Superior -200 -190 252 252 252 )252 252 of the Quaternary deposits in the county. The major sand bodies from this 25model2 are -200 Bedrock ) ) 394 ) 394 ) Plymouth Plymouth presence of thick lake sediment implies that this location was a low spot ) provenance associated with the "V" sequence units of central, north- deposits. § St. Francis Formation—Upper member -120 ¦ Terrace sand and gravelly sand (Surficial¦§ Geology unit)—Terrace sediment. Orono depicted on Plate 5, Sand-Distribution Model; the full model and all of the cross sections Qat Orono -200 -200 -170 Bedrock Loam to sandy loam diamict (Surficial Geology unit)—Till. on the landscape after the Superior lobe retreated. Other low areas on central, and east-central Minnesota (Meyer, 1997, 2016). -210 -200 Bedrock Unnamed Wayzata used to develop it can be accessed through the digital files of the Minnesota Geological Wayzata Qtt Qf1 Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand to -210 Bedrock 93°45' Outwash Qvo the landscape, including former tunnel valleys, also filled with this fine- Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand to 93°45' 93°45' 93°45' Superior 93°45' 93°45' Qlt Silty clay loam to silty clay (subsurface unit)—Fine-grained organic matter sandy gravel deposited by meltwater associated with the upper member of Qvo -210 -130 Brooklyn 169 Survey. The39 Quaternary4 geologic units shown on the cross sections were definedBrooklyn from 169 394 grained sediment as the Superior lobe continued to retreat to the northeast -220 Bedrock Brooklyn Brooklyn Brooklyn Brooklyn ¤ St. Louis ¦§ (sapropel) that may be massive or laminated; fine-grained sand, silt, and Qts2 Fine-grained¤ St. sand Louis to sandy§ gravel (subsurface unit)—Fine-grained sand sandy gravel deposited by meltwater associated with unnamed Superior- ¦ the St. Francis Formation. Discontinuous, and likely contains meltwater provenance Qot Till Parkinterpretation of new data collected for this study and from existing data and samples Park (Plate 3, Fig. 3B). Subsequently, this unit was eroded and incorporated Center Center Center Maple Center Center Center clay deposited in low areas along the upper terraces of the Mississippi to sandy gravel deposited by meltwater associated with the Twin Cities deposits associated with the overlying Sauk Centre Member of the Lake provenance sediment. Discontinuous, and likely contains meltwater -140 ) Maple Maple ) Maple )55 Maple ) from previous investigationsMaple (see Plate 3, Surficial Geology, Index to Previous Mapping). into the push moraine ice-contact deposits of the Twin Cities Member -230 55 ) ) 55 Bedrock 55 55 55 River. Brown to black where organic-rich, and gray-green-blue where Member of the New Ulm Formation. This sand unit is distinct from the Henry Formation. Outwash. deposits associated with the overlying Elmdale Formation. Outwash. Bedrock Grove Grove Grove These data sourcesGrove include: seven rotary-sonic)55 drill cores, archived split-spoon cores )55 Grove Undifferentiated sand Qsu psu suu suGrove Minnetonka unoxidized. This sediment was subsequently buried by terrace sandMinnetonka other Twin Cities Member sand units because it overlies a thick sequence of the New Ulm Formation (unit Qti). Cromwell Formation lacustrine Sandy loam diamict (subsurface unit)—Unsorted, reddish-brown to brown, Figure 7. Stratigraphic columns showing the Quaternary stratigraphy in five archived Figure 8. Stratigraphic columns showing the Quaternary stratigraphy from 19 drill holes at four sites, over 450 well cuttings sets archived in the Minnesota Sandy loam to loam diamict (subsurface unit)—Unsorted, calcareous, Qot 94 94 94 94 94 35W 94 of Cromwell Formation fine-grained35W sand and silt. It likely represents deposits Qsf1 split-spoon cores collected in the city of Independence (Fig. 1). The locations are ¦§ ¦§ ¦§ and gravel (unit Qat) because of fluctuating river levels at the end of the ¦§ commonly leached, yellowish-red (5YR 5/6) where oxidized, sandy loam sandy loam till of Superior provenance. This unit is mapped locally in in four archived split-spoon cores collected in the city of Corcoran ¦§ ¦§ ¦§ ¦§ ) Geological Survey cuttings library, outcrops, soil auger samples, and water-well and soil ) Undifferentiated Qu pu Qu ups ups Un St. Bonifacius 7 PleistoceneSt. BonifaciusEpoch. The thickest and most extensive of these deposits 7 proglacial outwash deposited when the Grantsburg sublobe advanced Qs2 Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand the deepest bedrock valleys. Where not overlain by Elmdale Formation clustered within a 0.5-mile (805-meter) radius and are labeled with their site name and (Fig. 1). The locations are clustered within a 0.5-mile (805-meter) T. 118 N. T. 118 N. boring drillers' logs (Plate 1, Data-Base Map). T. 118 N. to loam till of Superior provenance. This member contains slightly more T. 118 N. T. 118 N. 494 T. 118 N. Excelsior T. 28 N. was given the name Lake Bassett and is mappedExcelsior near Loring Park in into eastern Hennepin County, which was subsequently buriedT. 28 by N. Twin to sandy gravel deposited by meltwater associated with the St. Croix till, it likely includes sediment from the lower member of the St. Francis unique well number. The stratigraphy is based on texture and lithologic composition radius and are labeled with their site name and unique well number. 494 494 494 Bedrock Topography 494 )7 494 )7 abundant red and dark Precambrian very coarse sand grains and more 93°15' 93°15' 93°15' § 93°15' 93°15' 494 EdinaOn each of the cross sections shown, rotary-sonic holes, well cuttings sets, and 93°15' Cities MemberEdina till. The meltwater also eroded and incorporated the phase of the Cromwell Formation. Discontinuous, and may contain ¦ 494 § of the 1-2 millimeter very coarse-grained sand fraction (Table 1). Notable at this site ¦§ ¦ The stratigraphy is based on texture and lithologic composition of ¦§ ¦§ Basal sand and gravel ¦§ Minneapolis (Meyer, 1996). Portions of this unit may have been drained Formation. Till. ¤12 ¤ ¤12 New Hope zus ¤12 ¦§ ¦§ light-colored felsic lithologies than the lower member. In the northern New Hope ¤12 New Hope 12 New Hope R. 23 W. ¤12 New Hope water wells are displayed as black vertical lines;New the rotary-sonic Hope hole is labeled; wells R. 24 W. R. 23 W. R. 24 W. R. 23 W. R. 24 W. R. 23 W. R. 24 W. R. 24 W. R. 23 W. R. 24 W. and excavatedR. 23 W.as part of urban development. Slackwater lacustrine underlying fine-grained sand and silt, giving the unit a slightly finer- meltwater deposits of the Automba phase of the Cromwell Formation. Undifferentiated Pleistocene deposits is the truncation of the Sauk Centre Member of the Lake Henry Formation by the the 1-2 millimeter very coarse-grained sand fraction (Table 1). The with cuttings are shown with)62 a unique line symbol. Well elevation may not match the )62 part of the county, where the two members are most commonly in direct 44°52'30" 100 )77 deposits. 44°52'30" grained texture10 compared0 to the other Twin )Cities77 Member sand units. The uppermost portion of this unit was likely reworked by meltwater Cromwell Formation. The Cromwell Formation at this site contains an average of ice that deposited the Cromwell Formation at this site apparently Plymouth Plymouth Plymouth ) surface) elevationPlymouth on the cross-section line because data for each line are gathered from ) ) contact, it can be difficult to differentiate them using only well logs. Till. Qsu Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand Independence Plymouth Independence Independence Figure 2. Correlation diagram showing the stratigraphic position of all units in Hennepin County compared with equivalentPlymouth units mapped in Wright (Knaeble, 2013), Anoka Independence 5 Richfield 5 Sand above lacustrine sediment. Richfield of the advancing Grantsburg sublobe; this mixed-provenance sand and 10 percent carbonate in the very coarse-grained sand fraction, which is higher than did not erode the Sauk Centre Member of the Lake Henry Formation Independence Figure 1. Selected stacked surfaces from the land surface to the bedrock surface. Representative major sand bodies underlying Hennepin County are on the left, with the intervening till and fine-grained ¤ Independence New Brighton Formation (Johnson and others, 2016)—Sediment associated Lake Henry Formation—Meyer Lake Member to sandy gravel of unknown provenance deposited by meltwater. Sand. ¤52 ¤ ¤52 52 ¤ a distance of up to 0.15 mile (0.25 kilometer) from both the north and south sides¤52 of gravel would then correlate with the Hillside Sand defined in the New 52 (Meyer, 2013), Sherburne (Lusardi, 2013), Carver (Lusardi, 2009), and Scott (Lusardi and Tipping, 2006) Counties. Unit cg in Wright County is described on the Surficial 52 Eden with glacial Lake Anoka. Only remnant patches of the formation remain Eden Moland Member (Johnson and others, 2016)—The Moland Member of the the average for the Cromwell Formation in the county. This higher carbonate content to the same extent that it did at the Independence site. Cromwell sediment layers on the right. Reddish areas are where the surface of each unit is at higher elevations (lighter gray for the bedrock surface), and greenish areas are where each unit is at lower elevations the line, where the surface elevation may be higher or lower. Bedrock units and faults Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand Qu Undifferentiated Pleistocene sediment (subsurface unit)—Includes till, Prairie at the surface in the county because most of the sediment was washed Prairie New Ulm Formation in Hennepin County is mapped only in the western Brighton area (Johnson and others, 2016). Meltwater that deposited this Qh2 is the result of erosion and incorporation of the underlying carbonate-rich till of the Formation till averaged 8 percent carbonate in the very coarse- 100 100 )100 Geology plate as35 anW ice-contact unit but as outwash on the Quaternary Stratigraphy plate, so it is correlated with both the ice-contact (unit Qsi) and outwash (unit Qs2) units in described49 on4 Plate 2, Bedrock Geology, are labeled and shown10 at the0 base of the Quaternary 35W 494 to sandy gravel deposited by meltwater associated with the Meyer Lake bedded clay, silt, sand, and gravel of unknown provenance. Shown in ) 35W 100 35W 100 ) unit commonly eroded the underlying till with which it is associated (unit ) 35W ) 35W Sauk Centre Member. The surface of this erosion is indicated by a black jagged line. ) grained sand fraction, only slightly above the average for the county (darker gray/black for the bedrock surface). Units are superimposed onto the bedrock surface to emphasize their preferential preservation in bedrock depressions. ¦§ away when glacial Lake Anoka drained via the Mississippi River through part of the county. Evidence§ for the presence of the Moland Member is 212 ¦ ¦§ ¤ ¤212 places where well-log data were insufficient or absent, particularly in deposits. Vertical exaggeration is 50x for all cross sections to show the commonly thin, ¦§ Member of the Lake Henry Formation. Discontinuous, and likely contains ¦§ ¦§ ¦§ Hennepin County. Unit in Anoka County includes units , , and , and unit includes unit . The pre-late Wisconsinan Quaternary stratigraphy for Scott ¦§ ). St. Croix-phase outwash. 94 94 94 94 Qwl Qwn Qwi Qwt Qwr Qwd 94 equivocal. A till with low shale content (1 to 10 percent) in split-spoon Qcs (Table 1). Erosion did occur in core C-1011, however, because the § 94 the area in north Minneapolis known as the Camden Breach (Meyer and the deepest parts of bedrock valleys. Sediment. ¦ complex units of the Quaternary section. § meltwater deposits associated with the overlying upper member of the ¦§ ¦§ ¦§ 45° ¦§ ¦ 45° ) 45° 45° ) 45° )55 County was not differentiated to the same extent as other atlases. Unit in Scott County is the Pierce Formation, which may correlate with the Elmdale Formation (see Plate 45° ) cores from Independence (Table 1) is herein considered to be the Moland Sandy loam to loam diamict (subsurface unit)—Unsorted, calcareous, brown carbonate content in the very-coarse grained sand fraction increased 55 ) 55 ) 55 Hobbs, 1989; Meyer, 1998). Qcs 55 Qpc 55 ¤169 Bloomington 35W T. 27 N. ¤169 Bloomington 35W T. 27 N. T. 29 N. T. 29 N. Because Hennepin¦§ County has been highly populated for a long time, it is the most T. 29 N. Member, an interpretation that is extended¦§ along the length of the border (7.5YR 4/4) to dark yellowish-brown (10YR 4/4) where oxidized, very St. Francis Formation. Outwash. from 5 to 11 percent in the lower 6 feet (2 meters) of the Cromwell Minneapolis T. 29 N. Minneapolis T. 29 N. Minneapolis 4, Fig. 2). The subsurface extent of unit shown on Plate 4 of the Scott County Geologic atlas may include other Winnipeg-provenance units such as the Sauk Centre and Meyer T. 29 N. Minneapolis Qnd Sand and gravelly sand (Surficial Geology unit)—Sand and gravelly sand REFERENCES Minneapolis T3 Minneapolis data-dense county in the state. As a result, the cross sections were drawn with more Clay loam to loam diamict (subsurface unit)—Unsorted, calcareous, light Surface GREENFIELD with adjacent Wright County. In part this interpretation was made in an dark grayish-brown where unoxidized (10YR 3/2), sandy loam to loam Qml West East Formation till section. The surface of this erosion is indicated by a 394 Lake Members of the Lake Henry Formation. Some units shown in the diagram are not shown on the printed cross sections but appear in the digital files of other cross sections. facies of glacial Lake Anoka. elevation 394 Plymouth 394 Plymouth 394 Plymouth Plymouth 394 Plymouth 394 detail and complexity than isPlymouth possible in less-populated counties. However, where data effort to achieve consistency with the mapped distribution of the Moland till deposited during the St. Croix phase of the Superior lobe. Average brownish-gray (10YR 6/2) to light yellowish-brown (2.5Y 6/4) where Baker, R.W., Diehl, J.F., Simpson, T.W., Zelazny, L.W., and Beske-Diehl, S., 1983, Pre- black jagged line. ¦§ ¦§ ¦§ Very fine- to medium-grained sand (Surficial Geology unit)—Not portrayed (feet) G-1012 ¦§ Qnb ¦§ 242285 ¦§ are comparatively sparse, units are portrayed as continuous with relatively uniform Wisconsinan glacial stratigraphy, chronology, and paleomagnetics of west-central Orono Orono Orono Orono Orono Member in adjacent Wright County (Knaeble, 2013). However, no lithologic composition of the very-coarse grained sand fraction is shown in oxidized, dark gray (5Y 4/1) where unoxidized, olive (5Y 5/3) where 1,020 Depth Orono thicknesses and minimal changes in elevation. Glacial till and fine-grained lacustrine in cross-sections illustrated on this plate, but mapped elsewhere. Fine- reduced, clay loam to loam till. In general, the lower part of the unit Wisconsin: Geological Society of America Bulletin, v. 94, p. 1442-1449. (feet) Lithology evidence of oxidation, leaching, soil formation, or subaerial exposure is Table 1. Where the ice eroded and incorporated the underlying carbonate- 0 Wayzata Wayzata Wayzata Wayzata Wayzata Figure 3. Fine-grained sediment at or near the surface—Model-generatedsedimentsWayzata aremap generally showing considered the moreextent continuous and than sand and gravel units because of grainedFigure sand facies 4. of Surficialglacial Minnesota Lake sandAnoka. andRiver gravel Valley —Model-generatedLandslides | 17 map showing the extent and thickness of sand and locally contains more red Precambrian clasts and silt than the upper part. G-1007 present at the upper contact of this unit in the cores from Independence, rich, loamy tills of the Lake Henry Formation, the unit is loamier and more Hobbs, H.C., 1998, Use of 1-2 millimeter sand-grain composition in Minnesota Quaternary 1,010 Depth 242280 New Ulm Formation (Johnson and others, 2016)—Sediment associated with G-1002 394 thickness of surficial fine-grained sediment (units Ql, Qc, Qhl, Qsh, Qtcthe, Qtl way, andglaciers Qst deposited [and unitthese sedimentQp where types. it Till was typically laid down39 as laterally4 gravel bodies generally occurring at or near the land surface. Includeswhich would units be Qasexpected, Qag if ,it Qatwere, Qnddeposited, Qnb during, Qno an, Qtsearly, advance yellow than red. This unit may include sediment from the underlying The differences within the unit are the result of erosion and incorporation studies, in Patterson, C.J., and Wright, H.E., Jr., eds., Contributions to Quaternary (feet) Lithology Depth 242275 -10 169 394 169 394 169 394 ¤169 169 394 169 the Des Moines lobe and Grantsburg sublobe of Riding Mountain 0 (feet) Lithology ¤ ¤ St. Louis extensive sheets deposited directly by¤ ice. Sand and gravel were deposited by streams of underlying Superior-provenance sediment and interglacial lacustrine 1,000 St. Louis ¤ St. Louis St. Louis ¦§ ¤ St. Louis St. Louis of the Des Moines lobe. It is possible that this low-shale content till Lake Henry Formation tills, particularly in the southwestern quarter of studies in Minnesota: Minnesota Geological Survey Report of Investigations RI- ¦§ § ¦§ overlies them] from Plate 3, Surficial Geology) occurring at the land surface or below surface water. Also ¦§ , , , and the artificial fill associated with units , , and from Plate 3. 0 ¦ ¦§ Qhi Qti Qsi Ql Qti Qsi Park and therefore tend to be more discrete and discontinuous. By convention, subsurface provenance (Plate 3, Fig. 2). Variations in the amount of shale in the deposits (Table 1). This unit may correlate with the second member of the -20 Park Park Park Park Park was instead generated by ice associated with the Villard Member as it the county where underlying strata were thrusted and deformed at the 49, p. 193-208. G-1009 -10 DAYTON includes unit , which occurs just beneath surficial units and/or the artificial fill associated with unit . 990 Surface West East Qlt Qat sand and gravel units are associated with theQl till underlying the unit. However, these 1-2 millimeter very coarse-grained sand fraction are interpreted to be the informal Good Thunder formation identified in south-central Minnesota 242282 -10 advanced over the sandier units of the underlying Cromwell Formation. margin of the Superior lobe during this phase. St. Croix-phase till. Johnson, M.D., Adams, R.S., Gowan, A.S., Harris, K.L., Hobbs, H.C., Jennings, C.E., Depth elevation result of differential incorporation of underlying Quaternary deposits, (feet) Lithology -30 D-1010 sand and gravel units likely represent deposition by meltwater from ice that deposited (Johnson and others, 2016). Till. Knaeble, A.R., Lusardi, B.A., and Meyer, G.N., 2016, Quaternary lithostratigraphic -20 (feet) Qms Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained Qs3 Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand to 0 Depth 242248 ) both the underlying and overlying till units. An exception was made to this convention which is how the mixed provenance Twin Cities Member (unit Qtt) was 980 -20 930 Lithology )55 ) ) 55 ) )55 St. Francis Formation—Lower member units of Minnesota: Minnesota Geological Survey Report of Investigations RI-68, Minnetonka Minnetonka 55 Minnetonka 55 Minnetonka Minnetonka 55 Minnetonka sand to sandy gravel deposited by meltwater of the Des Moines lobe. sandy gravel deposited by meltwater associated with the Emerald phase of -40 (feet) where data were sufficient to make that determination (such as unit Qts2). Most of the formed (see Plate 3 for a more detailed explanation of the glacial history). -30 0 Discontinuous, and may contain meltwater deposits of the overlying the Cromwell Formation. Discontinuous, and likely contains meltwater Qf2 Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand 262 p. -10 35W 35W 35W 35W units from the Late Pleistocene and Holocene Epochs described on Plate 3 match the35 W In addition to the Twin Cities Member, Riding Mountain-provenance 970 G-1001 -30 920 35W Villard Member of the New Ulm Formation. Sand. deposits of the overlying St. Croix phase of the Cromwell Formation. to sandy gravel deposited by meltwater associated with the lower St. Knaeble, A.R., 2013, Quaternary stratigraphy, pl. 4 of Tipping, R.G., project manager, -50 § Depth 242274 -10 ¦ -40 ¦§ tills with low (unit ), moderate (unit ), and high shale (unit ) ¦§ -20 ¦§ units mapped on this plate. The exceptions are Holocene peat (unit ) and lacustrine ¦§ ¦§ Qmt Qvt Qht ) Qp D-1007 ) ) ) 93°30' St. Bonifacius 93°30' 93°30' ) 93°30' ) 93°30' Sandy loam diamict (subsurface unit)—Unsorted, calcareous, very dark Meltwater that deposited this unit commonly eroded the underlying till Francis member of the St. Francis Formation. Discontinuous, and likely Geologic atlas of Wright County, Minnesota: Minnesota Geological Survey County (feet) Lithology St. Bonifacius 7 St. Bonifacius 7 St. Bonifacius 7 7 St. Bonifacius 7 St. Bonifacius 7 93°30' content were identified. The low shale unit may have been deposited in a Qmt 960 -40 910 242245 deposits (unit Ql), which are combined into unit Ql. Artificial fill related to units Ql, Qti, with which it is associated (unit ). Emerald-phase outwash. contains meltwater deposits associated with the overlying Meyer Lake 0 -60 Depth gray (2.5Y 3/1), sandy loam till. Contains common pebbles and cobbles; Qce Atlas C-30, 6 pls., scale 1:100,000. -50 -20 (feet) Lithology Excelsior T. 28 N. Excelsior T. 28 N. Excelsior T. 28 N. Excelsior T. 28 N. T. 28 N. Excelsior and Qsi is displayed by a stippled pattern. Additional Late Pleistocene and older units separate, earlier advanceT. 28 of theN. Des Moines lobe. The other two members -30 Excelsior R. 23 W. R. 22 W. Sandy loam to loam diamict (subsurface unit)—Unsorted, calcareous, brown Member of the Lake Henry Formation. Outwash. -50 0 ) ) R. 23 W. R. 22 W. ) R. 23 W. R. 22 W. R. 23 W. R. 22 W. ) R. 23 W. R. 22 W. R. 23 W. R. 22 W. boulders are less common. Average lithologic composition of the very Qce Knaeble, A.R., and Meyer, G.N., 2007, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., 950 -10 900 7 Edina )7 Edina 7 Edina 7 Edina )7 Edina 7 are present only in the subsurface and are thus mappedEdina and described exclusively on and the Twin Cities Member are interpreted to have been deposited as -70 494 494 494 494 coarse-grained sand fraction is shown in Table 1. Till. (7.5YR 4/4) to dark yellowish-brown (10YR 4/4) where oxidized, very Qsf2 Sandy loam diamict (subsurface unit)—Unsorted, calcareous, commonly project manager, Geologic atlas of Todd County, Minnesota: Minnesota Geological -40 -60 -30 494 93°37'30" 93°37'30" 93°37'30" 494 93°37'30" 93°37'30" this plate. Areas below the depth of available water-well records and above the bedrock one continuous event (Fig. 2; Plate 5, 93°37'30"Fig. 2). -10 ¦§ dark grayish-brown where unoxidized (10YR 3/2), sandy loam to loam leached, yellowish-red (5YR 5/8) to reddish-yellow (7.5YR 6/6) where 940 -60 ¦§ § ¦§ Survey County Atlas C-18, 6 pls., scale 1:100,000. -20 ¦ Cromwell Formation (Johnson and others, 2016)—Sediment associated with ¦§ 101 § 101 -80 ¦ 890 )101 )101 )101 ) surface are)10 mapped1 as "undifferentiated sediment" (unit ). For the most part, this ) T. 120 N. T. 120 N. T. 120 N. T. 120 N. T. 120 N. Qu Qno Fine-grained sand to sandy gravel (Surficial Geology unit)—New Ulm T. 120 N. -40 ) ) ) )62 ) the Superior lobe of Superior provenance (Plate 3, Fig. 2). Includes till associated with the Emerald phase of the Superior lobe. This unit oxidized, sandy loam to loam till of Superior provenance. The lithologic Lisiecki, L.E., and Raymo, M.E., 2005, A Pliocene–Pleistocene stack of 57 globally -50 -70 D-1001 ) unit is constrained to the deepest parts of the numerous bedrock valleys in the county. -20 62 62 62 62 62 Formation outwash—undifferentiated. -70 Depth 242239 ) is lithologically similar to the St. Croix-phase till of the Superior lobe composition was averaged from four leached and four unleached samples. 18 -30 )77 ) 77 )77 sediment deposited during the Emerald, St. Croix, and Automba phases of -90 D-1014 ) 77 distributed benthic O records: Paleoceanography, v. 20, no. 1, p. 1-17. 880 Lithology 77 )77 (feet) 44°52'30" 100 44°52'30" 100 44°52'30" 100 44°52'30" )100 44°52'30" 100 44°52'30" Figure 2 is a time–distance illustration showing the inferred)100 relationships between Heiberg Member (Johnson and others, 2016)—The till of the Heiberg Member δ -60 -80 -50 242252 ) ) Depth ) 93°22'30" (unit ), and may contain even more locally-derived sediment from The lower member contains slightly less red and dark Precambrian very 0 93°22'30" ) 93°22'30" ) ) Rogers ) Rogers 93°22'30" Rogers 93°22'30" Rogers Rogers) 93°22'30" Rogers the Superior lobe during the late Wisconsinan glaciation. The till of the Qcs -80 -30 ) 5 ) age, provenance, stratigraphic position, and general geographic location of the sediments Lusardi, B.A., 2013, Quaternary stratigraphy, pl. 4 of Lusardi, B.A., project manager, (feet) Lithology 5 Richfield 5 5 Richfield Richfield 5 5 Richfield of the New Ulm Formation in Hennepin County has the greatest abundance -40 -100 D-1002 Richfield Richfield Cromwell Formation in Hennepin County is atypical because it contains underlying Quaternary or Paleozoic bedrock units. In most areas the unit coarse sand grains and more light-colored felsic lithologies than the 870 Geologic atlas of Sherburne County, Minnesota: Minnesota Geological Survey -70 -90 -60 Depth 242240 0 deposited by major glacial episodes (supplementary information on Plate 3, Fig. 2; Table of shale (34 percent) in the county, although it is less than the defined -10 94 94 94 94 94 94 an average of 6 percentR. 21 Paleozoic W. carbonate in the 1-2 millimeter very has a patchy distribution, with more continuous and abundant deposits upper member. This may be the result of mixing with underlying Rainy- -90 -40 (feet) Lithology ¦§ R. 21 W. ¦§ R. 21 W. ¦§ R. 21 W. ¦§ 1). Descriptions¦§ from the four rotary-sonic drill cores contractedR. 21 W. by the Minnesota average of 41 percent (Table 1; Johnson and others, 2016).¦§ County Atlas C-32, 5 pls., scale 1:100,000. -50 Eden Eden Eden Eden Eden Eden present in the southeastern part of the county near Bloomington and the provenance sediment. The subtle compositional differences between the -110 0 coarse-grained sand fraction (Table 1). From northeast to southwest, the -80 -100 860 -70 -10 Prairie Geological Survey appear in Figures 3 through 6, and the texture and composition of Lusardi, B.A., and Tipping, R.G., 2006, Quaternary stratigraphy, pl. 4 of Setterholm, -20 Prairie Prairie Prairie Prairie Prairie Qhl Silty clay loam to silt loam (Surficial Geology unit)—Lacustrine deposits. former flow direction of the Superior lobe, the carbonate content in the very southwestern part of the county near St. Bonifacius. Definition of two members of the St. Francis Formation make it difficult to differentiate -100 -50 R. 24 W. R. 24 W. R. 24 W. R. 24 W. R. 24 W. selected geologic units are summarized in Table 1. Because most samples of pre-late R. 24 W. D.R., project manager, Geologic atlas of Scott County, Minnesota: Minnesota -60 -120 -10 494 494 494 494 494 R. 21 W. 494 Cromwell Formation increases by an average of 10 percent (from 3 to this unit was based primarily on the presence of a sand body between them with well logs alone. Till. -90 -110 -80 -20 ¤169 ¤169 ¤169 ¤169 Wisconsinan strata were taken from the 19 archived¤169 split-spoon core holes, the interpreted ¤169 Geological Survey County Atlas C-17, 6 pls., scale 1:100,000. -30 § Surficial Geology Ice-contact deposits. -110 ¦ Loamy sand to gravelly sand ( unit)— 212 ¦§ -60 ¦§ 212 212 § Qhi ¦ what was described in well logs as two red or rocky clays. Emerald- ¦§ 212 ¤ ¤ 212 ¦§ ¤ 212 52 ¤ ¤ ¤ ¤ Unnamed formation of Rainy provenance ¤ 52 ¤ ¤ 52 13 percent, for example). This increase is interpreted to be the result of -70 ¤ 52 52 ¤ 52 stratigraphy for each of the holes at their four respective sites is shown in Figures 7 -130 -20 phase till. Meyer, G.N., 1986, Subsurface till stratigraphy of the Todd County area, central Minnesota: -100 -120 -90 -30 Osseo 45°7'30" Osseo 45°7'30" Osseo 45°7'30" Osseo 45°7'30" Osseo theOsseo Superior lobe eroding and incorporating45°7'30" sediments of the underlying Qwo Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand to -40 through 10. Radiocarbon dates of organic material collected from rotary-sonic45°7'30" cores and Silt loam, sandy loam, and loamy sand and gravel (Surficial Geology Minnesota Geological Survey Report of Investigations RI-34, 40 p. -120 -70 Qsh carbonate-rich tills of the Lake Henry Formation. A similar increase in Pre-late Wisconsinan -80 -140 during fieldwork appear in Table 2. A diagram correlating the units mapped in Hennepin sandy gravel deposited by meltwater from an ice lobe of Rainy provenance. -30 Bloomington Bloomington Bloomington T. 119 N. 169 BloomingtonT. 119 N. T. 119 N. Bloomington T. 119 N. BloomingtonT. 119 N. unit)—Stagnation deposits. T. 119 N. ———1996, Geology of the Bassett valley area: Minnesota Geological Survey Open- -110 -130 -100 -40 ¤169 35W 169 169 35W ¤ 35W T. 27 N. 169 ¤169 35W T. 27 N. carbonate content of the Cromwell Formation in Stearns County is the Lake Henry and St. Francis Formations (Johnson and others, 2016)—Sediment Discontinuous, and likely contains meltwater deposits associated with -130 -50 T. 27 N. 35W ¤ -80 ¤ T. 27 N. T. 27 N. ¤ 35W County with those in adjacent counties is included on Plate 5. 252 252 252 T. 27 N. )252 252 252 -90 ) ) ¦§ ) ) Qht Loam to clay loam diamict (Surficial Geology unit)—Till. result of mixing with the underlying) carbonate-bearing Hewitt Formation, File Report 96-3, 6 p. -150 -40 ¦§ ¦§ ¦§ of Winnipeg and Superior provenance, respectively (Plate 3, Fig. 2). The the overlying lower member of the St. Francis Formation. Shown only ¦§ § -140 ¦ -50 -120 -110 Villard Member (Johnson and others, 2016)—The till of the Villard Member and in Washington County from incorporating the underlying Lake Henry ———1997, Pre-late Wisconsinan till stratigraphy of north-central Minnesota: Minnesota -140 -60 93°45' 93°45' 93°45' 93°45' 93°45' 93°45' vast majority of the pre-late Wisconsinan Quaternary deposits mapped in on Figure 9. Outwash. -90 Brooklyn ACKNOWLEDGEMENTS -100 -160 Brooklyn Brooklyn Brooklyn Brooklyn of the New Ulm Formation in Hennepin County contains the defined Formation and PaleozoicBrooklyn carbonate bedrock (Johnson and others, 2016; Hennepin County are composed of four intercalated members of these Geological Survey Report of Investigations RI-48, 67 p. -150 -50 Center Qwt Sandy loam to loam diamict (subsurface unit)—Unsorted, calcareous, -130 -120 -60 Maple Center Maple Center Maple Center Maple Thanks to the City of Tonka Bay, the Parks and Recreation DepartmentCenter of Minneapolis, average of 19 percent shale (Table 1; Johnson and others, 2016). This Maple Center -150 -70 )55 )55 )55 )55 )55 Maple )55 Meyer, 2016). two formations. The Lake Henry Formation consists of two members: commonly leached, brown (7.5YR 4/4) to olive-brown (2.5Y 4/4) where ———1998, Glacial lakes of the Stacy basin, east-central Minnesota and northwest -110 -100 Grove Grove Grove Grove Grove Grove -170 -60 and to landowners for allowing rotary-sonic drilling on their property. Gary Meyer and member is interpreted to be gradational with the Twin Cities Member Wisconsin, in Patterson, C.J., and Wright, H.E., Jr., eds., Contributions to Quaternary -140 -160 -70 94 94 Qsi Loamy sand to sandy94 gravel (Surficial Geology unit)— Artificial fill the Sauk Centre and the Meyer Lake. These two members have nearly oxidized, very dark brown (10YR 2/2) where unoxidized, sandy loam -130 Bedrock ¦§ ¦§94 ¦§94 ¦§ Andrew Retzler of the Minnesota Geological Survey helped94 with coordinating drilling of the New Ulm Formation, deposited when the Grantsburg sublobe ¦§ -160 -80 ¦§ -120 -110 associated with this unit is shown with a stippled pattern. Ice-contact identical texture but differ lithologically (Table 1). The 1-2 millimeter to loam till of Rainy provenance. The lithologic composition, based on studies in Minnesota: Minnesota Geological Survey Report of Investigations RI- Bedrock -180 Bedrock T. 118 N. T. 118 N. T. 118 N. T. 118 N. T. 118 N. T. 118 N. -170 -70 494 494 494 494 sites. Minnesota Geological49 Survey4 staff members Matthew Ettsen, Zachary Van Orsdel, advanced into Hennepin County and flowed northeastward. 494 deposits. very coarse-grained sand fraction of the Meyer Lake Member contains 49, 208 p. -150 -140 -80 93°15' 93°15' 93°15' ¦§ 93°15' 93°15' 93°15' one sample, differs from that of the lower member of the St. Francis -170 ¦§ ¦§ ¦§ ¤ ¦§ ¦§ -90 ¤12 New Hope Figure 8. SandR. 23 andW. gravel unit¤12 —Model-generated map of the extent,New depth Hope from the surface, and thickness¤12 Figure 9. Sand and gravel unitNew Hope —Model-generated map of the extent,12 depth from the surface, and thicknessNew Hope FigureR. 24 W. 10.R. 23 W.Sand and gravel¤12 unit —Model-generatedRyan Puzel, and Emily Bauer provided map support ofNew during the Hope rotary-sonic extent, drilling. depth Numerous from the Fine-grained surface, sand¤12 toand sandy gravel (subsurface unit)—Fine-grained sand New Hope R. 24 W. R. 23 W. less carbonate and more Precambrian crystalline and red grains compared -130 -190 Figure 5. Sand and gravel unit —Model-generated map of the extent, depth from the surface, and thickness Figure 6. Ice-contact sand and gravel unit —Model-generated map of the extent, depth from the surface, Figure 7. Sand and gravel unit —Model-generated map of the extent, depth from the surface, and thickness R. 24 W. Qs2 R. 24 W. R. 23 W. Qs3 R. 24 W. R. 23 W. Qf1 R. 24 W. R. 23Qvs W. Qs1 Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand to Formation because it contains fewer red grains indicative of Superior ———2013, Quaternary stratigraphy, pl. 4 of Setterholm, D.R., project manager, Geologic -180 -80 Qvs Qsi Qs1 water-well companies contributed the subsurface information used in this atlas, and -160 -90 Plymouth Plymouth Plymouth Plymouth Plymouth to sandy gravel deposited by meltwater of the Grantsburg sublobe. Plymouth sandy gravel deposited by meltwater associated with the Automba phase to the Sauk Centre Member. This reflects more mixing with underlying provenance (Table 1). This unit was recognized in the subsurface only atlas of Anoka County, Minnesota: Minnesota Geological Survey County Atlas -100 Bedrock Independence Independence Independence Independence Independence Independence -140 of sand¤52 and gravel bodies stratigraphically immediately above till of unit and¤ 52below till of unit and of sand and gravel bodies stratigraphically¤52 immediately above till of unit and below till of unit . It ¤thickness52 of sand and gravel bodies stratigraphicallyspecial thanks are immediately given to those who have abovedonated drill tillcuttings of over¤ 52unit the years to the and belowDiscontinuous, till of andunit may contain meltwater deposits of the overlying ¤52 sediment of Superior provenance. These compositional differences are -200 of sand and gravel bodies stratigraphically immediately above till of unit Qvt and below till of unit Qht. This and thickness of ice-contact sand and gravel bodies stratigraphically atop all other sediments associated with the of sand and gravel bodies stratigraphically immediately above till of unit Qca and below till of units Qvt and Qcs Qca Qce Qcs Qsf1 of the Cromwell Formation. Discontinuous, and may contain meltwater in a few places within the deepest bedrock valleys in the western part C-27, 6 pls., scale 1:100,000. -170 -190 -90 Bedrock Minnesota Geological Survey. Heiberg Member of the New Ulm Formation. Sand. subtle and variable, which can make it difficult to differentiate these )100 35W )100 35W )100 35W )100 35W )100 35W deposits of the)10 overlying0 Villard or Twin Cities35 MembersW of the New of the county. Shown only on Figure 9. Till. ———2016, Quaternary stratigraphy, pl. 4 of Bauer, E.J., project manager, Geologic -150 -110 ¦§ ¦§ ¦§ ¦§ ¦§ ¦§ -210 members from one another in the subsurface on this basis alone. However, -200 unit is generally discontinuous; however, thicker and more extensive areas of this sand tend to occur near the Cromwell Formation and beneath all sediments associated with the New Ulm Formation. In places, it may overlie . In places, it may overlie older, deeper units. This unit was deposited by meltwater streams emanating from sediment94 of the New Ulm Formation. In places, it may overlie older, deeper units.94 This unit was deposited commonly overlies sediment of older, deeper94 units. This unit was deposited by meltwater streams emanating ¦§94Qsc. In places, it may overlie older, deeper units. This unit was deposited by meltwater94 from Qvt a pre-Wisconsinan Loam to sandy loam diamict (Surficial Geology unit)—Till. Ulm Formation. This unit includes¦§94 proglacial outwash and ice-contact Elmdale Formation (Johnson and others, 2016)—Sediment of Winnipeg atlas of Washington County, Minnesota: Minnesota Geological Survey County Atlas -180 Qtt ¦§ 45° ¦§ ¦§ ) 45° ¦§ 45° )55 )55 45° )55 45° 55 DESCRIPTION OF)55 CROSS-SECTION UNITS 45° )55 in Hennepin County, as in adjacent Anoka (Meyer, 2013) and Sherburne Bedrock -120 T. 29 N. T. 29 N. Twin Cities Member (Johnson and others, 2016)—The Twin Cities Member sand and gravel, the latter of which is most abundantT. within 29 N. the Elm provenance (Plate 3, Fig. 2) associated with the "W" sequence units C-39, 6 pls., scale 1:100,000. -160 Bedrock -220 Minneapolis Minneapolis T. 29 N. Minneapolis T. 29 N. Minneapolis Minneapolis T. 29 N. Minneapolis -210 by meltwater streams emanating from the ice margin when the Superior lobe retreated during the St. Croix from the ice margin when the Superior lobe retreated during the Emerald phase. It may have also been deposited ice advance of Superior provenance. It may alsoEach unit include on the cross sectionssand is andplaced ingravel one of three associated categories, as indicated with the overlying pre- Creek Park Reserve in Maple Grove. Linear, sinuous ridges previously (Lusardi, 2013) Counties, the two members are discontinuously separated -190 outer extent of unit Qvt. older, deeper units. This unit, deposited at former ice margins of the Superior lobe, is commonly excavated for the ice margin when the Superior lobe retreated during the Automba phase. It may394 have also been deposited 394 394 394 Plymouth 394 of the New Ulm Formation in Hennepin394 County contains about equal Plymouth of central and north-central Minnesota (Meyer, 1997). The Elmdale Meyer, G.N., and Hobbs, H.C., 1989, Surficial geology, pl. 3 of Balaban, N.H., project ¦§ Plymouth ¦§ Plymouth ¦§ Plymouth ¦§ § Plymouth ¦§ by the upper member of the St. Francis Formation. The Meyer Lake -230 Bedrock -130 ¦ identified to be eskers within that park (Meyer and Hobbs, 1989) may in parentheses after the description: Surficial Geology unit—a unit having an identical proportions of shale and red grains in the very coarse-grained sand Formation may correlate with the Pierce Formation mapped in Washington Orono Orono Orono Orono Orono Orono manager, Geologic atlas of Hennepin County, Minnesota: Minnesota Geological -200 aggregate because it is very thick and contains a significant proportion of coarse-grained gravel and cobbles. subglacially during the Automba-phase advance within tunnel valleys as eskers or stream sediment. phase. It may also have been deposited subglacially during the St. Croix-phase advance within tunnel valleys proglacially when the Superior lobe advanced during the St. Croix phase. Additionally, it may have been Wisconsinan ice advance of Winnipeg provenance.description, label, and color as on Plate 3, Surficial Geology (see Plate 3 for detailed fraction, indicating mixed Riding Mountain and Superior provenance be eskers associated with this phase of the Superior lobe, which were Member is underlain by the lower member of the St. Francis Formation. (Meyer, 2016) and Scott (Lusardi and Tipping, 2006) Counties (Fig. 2). Wayzata Wayzata Wayzata Wayzata Wayzata Wayzata Survey County Atlas C-4, pt. A, 9 pls., scale 1:100,000. -140 descriptions); subsurface unit—a unit that is depicted only in the subsurface that has a (Table 1). It was generated by ice carrying sediment of Villard Member subsequently buried by at least 30 feet (9 meters) of Grantsburg sublobe The upper and lower members of the St. Francis Formation are texturally 394 394 394 169 394 394 Qeo Fine-grained sand to sandy gravel (subsurface unit)—Fine-grained sand Reimer, P.J., 2012, Refining the radiocarbon time scale: Science, v. 338, p. 337-338. -210 ¤169 St. Louis as¦§ eskers or stream sediment. ¤169 St. Louis deposited subglacially during¤169 theSt. Louis Emerald-phase advance within tunnel valleys as eskers or stream sediment.¤ St. Louis ¦§ ¤169 St. Louis 394 ¤169 St. Louis ¦§ and lithologically similar; however, the lower member contains more ¦§ ¦§ till. It is also possible that these ridges are Grantsburg sublobe recessional unique label and color; or modified unit—multiple units from Plate¦§ 3 that are combined lithologic composition. Park Park Park Park Park Park to sandy gravel deposited by meltwater associated with the Elmdale Stuiver, M., Reimer, P.J., and Reimer, R.W., 2017, CALIB radiocarbon calibration -150 into one unit on the cross sections. ice margins, or a combination of both. Automba-phase outwash and light-colored felsic grains and fewer red and dark grains. -220 Bedrock Bedrock Qts Fine-grained sand to sandy gravel (Surficial Geology unit)—Outwash. Formation. Discontinuous, and likely contains meltwater deposits program: Calib7.1, accessed December, 2017,
Figure 12. Sand and gravel unit —Model-generated map of the extent, depth from the surface, and Figure 13. Sand and gravel unit —Model-generated map of the extent, depth from the surface, and Figure 14. Sand and gravel unit —Model-generated map of the extent, depth from the surface, and Figure 16. Number of sands bodies—Model-generated map of the extent and number of Quaternary sand Figure 11. Sand and gravel unit Qh2—Model-generated map of the extent, depth from the surface, and Qf2 Qeo Qvo Figure 15. Undifferentiated sediment—Model-generated map of the extent, depth from the surface, and thickness of sand and gravel bodies stratigraphically immediately above till of unit and below till of unit thickness of sand and gravel bodies stratigraphically immediately above till of unit and below till of units thickness of sand and gravel bodies stratigraphically immediately above till of unit and below till of unit bodies (as defined in the model) encountered between the land surface and bedrock. The individual sand bodies thickness of sand and gravel bodies stratigraphically immediately above till of unit Qml and below till of unit Qsf2 Qet Qot thickness of Quaternary sediment for which little or no descriptive data are available. This unit is typically . In places, it may overlie older, deeper units. This unit was deposited by meltwater from a pre-Wisconsinan , and more commonly, unit . In places, it may overlie older, deeper units. This unit was deposited by Qet. In places, it may overlie older, deeper units. This unit was deposited by meltwater from a pre-Wisconsinan restricted to the deepest portions of bedrock valleys. are not necessarily interconnected. Uncolored areas have no mapped sand units. Figure 12. Sand and gravel unit Qf2—Model-generated map of the extent, depth from the surface, and Figure 13. Sand and gravel unit Qeo—Model-generated map ofQsf1 the. In places,extent, it may depth overlie older, from deeper the units. surface, This unit wasand deposited by meltwaterFigure from a 14.pre-Wisconsinan Sand and gravelQml unit Qvo—Model-generated map of the extent, depth from the surface,Qwt and FigureQsf2 15. Undifferentiated sediment—Model-generated map of the extent, depth from the surface, and Figure 16. Number of sands bodies—Model-generated map of the extent and number of Quaternary sand Figure 11. Sand and gravel unit Qh2—Model-generated map of the extent, depth from the surface, and ice advance of Winnipeg provenance. It may also include sand and gravel associated with the overlying pre- ice advance of Superior provenance. It may also include sand and gravel associated with the overlying pre- meltwater from a pre-Wisconsinan ice advance of Winnipeg provenance. It may also include sand and gravel ice advance of Superior provenance. It may also include sand and gravel associated with the overlying pre- thickness of sand and gravel bodies stratigraphically immediately above till of unit and below till of unit thickness of sand and gravel bodies stratigraphically immediately above till of unit and below till of units thickness of sand and gravelWisconsinan bodies ice stratigraphically advance of Winnipeg provenance. immediately Commonly above preserved till in bedrockof unit valleys. and below till ofassociated unit with the overlying pre-Wisconsinan ice advances of Rainy and Superior provenance. Commonly Wisconsinan ice advance of Winnipeg provenance. Commonly preserved in bedrock bodiesvalleys. (as defined in the model) encountered between the land surface and bedrock. The individual sand bodies thickness of sand and gravel bodies stratigraphically immediately above till of unit Qml and below till of unit Qsf2 Wisconsinan ice advance Qetof Superior provenance. Commonly preserved in bedrock valleys. Qot thickness of Quaternary sediment for which little or no descriptive data are available. This unit is typically preserved in bedrock valleys. Qml. In places, it may overlie older, deeper units. This unit was deposited by meltwater from a pre-Wisconsinan Qwt, and more commonly, unit Qsf2. In places, it may overlie older, deeper units. This unit was deposited by Qet. In places, it may overlie older, deeper units. This unit was deposited by meltwater from a pre-Wisconsinan restricted to the deepest portions of bedrock valleys. are not necessarily interconnected. Uncolored areas have no mapped sand units. Qsf1. In places, it may overlie older, deeper units. This unit was deposited by meltwater from a pre-Wisconsinan Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the ice advance of Winnipeg provenance. It may also include sand and gravel associated with the overlying pre- ice advance of Superior provenance. It may also include sand and gravel associated with the overlying pre- meltwater from a pre-Wisconsinan ice advance of Winnipeg provenance. It may also include sand and gravel ice advance of Superior provenance. It may also include sand and gravel associated with the overlying pre- Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources ©2018 by the Regents of the University of Minnesota Wisconsinan ice advance of Winnipeg provenance. Commonly preserved in bedrock valleys. ENVIRONMENT include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has Wisconsinan ice advance of Superior provenance. Commonly preserved in bedrock valleys. Wisconsinan ice advance of Winnipeg provenance. Commonly preserved in bedrock valleys. associated with the overlying pre-Wisconsinan ice advances of Rainy and Superior provenance. Commonly GIS compilation by R.S. Lively AND NATURAL RESOURCES been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation preserved in bedrock valleys. The University of Minnesota is an equal opportunity educator and employer Edited by Lori Robinson GEOLOGIC ATLAS OF HENNEPIN COUNTY, MINNESOTA TRUST FUND shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification. Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources ©2018 by the Regents of the University of Minnesota ENVIRONMENT include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has GIS compilation by R.S. Lively AND NATURAL RESOURCES been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation The University of Minnesota is an equal opportunity educator and employer Edited by Lori Robinson GEOLOGIC ATLAS OF HENNEPIN COUNTY, MINNESOTA TRUST FUND shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification. Figure 6.5a — Springs in Eroded Traces of Arcuate Depressions In Bloomington, iron-rich springs emerge where sands overlies lake clay of the Cromwell Formation and where numerous, deep-seated landslides have been mapped.
Figure 6.5b — Arcuate Depressions at the Head of a Landslide Area Three, arcuate, downhill- facing depressional features are present in the area where numerous, deep-seated landslides have been mapped.
Figure 6.5c — Downhill-facing Scarps are Indicative of Ancient, Deep- seated Landslides From Uchida et al., 2011.
18 | Hennepin County Landslide Hazard Atlas Table 6.2 — Cross sections, Units Involved in Recommendations Failure and Area Affected Landslide-susceptible areas like Line number Possible failure units Area these deep-seated failures can be 102 qts, qcl, qvt Western edge of County of two main types with differing 102 qts2 Eastern edge of County failure mechanisms. The extent of 102 qvt, qts2 Nine Mile Creek area affected at the top and toe 104 qat, qts Western edge of County of the bluff and the rate of failure 104 qts, qtt Eastern edge of County should both be considered when 101 qts, qtt, qcl Eastern edge of County assessing the hazard. Infrastructure 101 qts, qts2, qtt Nine Mile Creek and buildings on top of or on a slope 101 qts Purgatory Creek where springs are present, or where there are failure deposits and scarps, 101 qts Western edge of County should be evaluated to determine 100 qts, qvt, qcl Western edge of County if the site should be monitored to 100 qts Purgatory Creek detect ongoing motion (e.g., using 100 qts1 Nine Mile Creek tensiometers or inclinometers). 100 qts1, qcl Eastern edge of County Setbacks from the bluff top in 103 qcl Eastern edge of County these settings are overly simplistic 103 qcl, qts2 Nine Mile Creek approaches that do not work well with 103 qvt, qcl Western edge of County deep-seated features. Guidelines need 105 qts Western edge of County to be tailored to the geotechnical 105 qts Eastern edge of County needs specific to each region. 9 9 qvs, qvt Far western edge of County 9 9 qts, qts1, qvt Western edge of County To reduce the likelihood of failures in 9 9 qts Purgatory Creek the thick, dry sand deposits along the 9 9 qts, qst Eastern edge of County Minnesota River valley, preserving the 9 9 qat Nine Mile Creek slope angle is of critical importance. 8 9 qcl, qcs, qts Eastern edge of County Slope erosion can be reduced by 8 9 qts Nine Mile Creek protecting the toe of the slope, 8 9 qvt, qts Purgatory Creek controlling runoff above or onto 8 9 qts, qas Riley Creek east the slope, avoiding cuts into the slope without the use of engineered 8 9 qts, qht, qvs Riley Creek west retaining walls or other mitigation 8 9 qht Minnesota Bluff Trail measures, and keeping slopes 7 9 qht, qvs Riley Creek far west properly vegetated. 7 9 qht, qvs Riley Creek west 7 9 qht, qvs, qts Riley Creek east 7 9 qts, qvt Purgatory Creek 7 9 qts, qcl Eastern edge of County 6 9 qts Eastern edge of County 6 9 qts, qtl Purgatory Creek 6 9 qtc Interior of County 5 9 qtc, qht Interior of County 5 9 qts Eastern edge of County 4 9 qts, qcl Eastern edge of County 4 9 qht, qts Interior of County 3 9 qts, qtt, qcl Eastern edge of County 2 9 qtt, qcl Eastern edge of County 1 9 qcs Eastern edge of County 0 9 qts1, qcl, qcs, qs3 Eastern edge of County
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