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ABSTRACT

This field guide examines the evidence for multiple readvances of the Superior lobe, as well as the morphological and sediment record of glacial lakes in the western Lake Superior basin. During each readvance of the Superior lobe, ice went a shorter distance, reached a lower elevation, and laid down a finer-grained till due to incorporation of proglacial lake sediment. There are three distinct tills, which are correlated to three readvance phases: the St. Croix/Automba, Split Rock, and Nickerson. A red clay typically caps the stratigraphy at lower elevations in the basin. This clay may be a fourth till associated with a late readvance, perhaps equivalent to the Marquette phase in eastern Lake Superior. Alternatively, the red clay may be lacustrine. At issue are the potential hydraulic connections between glacial Lake Agassiz and the Atlantic Ocean during, and after, the Younger Dryas, because a readvance would fill the western Superior basin with ice and prohibit eastern Lake Agassiz drainage. Additional stops highlight the strandline and sediment record of the youngest glacial lake phase (glacial Lake Duluth), including the inspection of Lake Superior sediment cores that are archived at the National Lacustrine Core Repository in Minneapolis. The goals of the selected stops are to underscore the current understanding of the late glacial history of the western Superior basin and to provide new insights to spark discussion.

Geologic Background

The Superior Ice Lobe and Evidence for Multiple Readvances

The Superior lobe is one of multiple late Wisconsinan lobes recognized in Minnesota, each of which is characterized by a related set of glacial landforms, ice flow directions, till composition, and advance/retreat history (Fig. 1) (Wright 1972; Patterson and Johnson, 2004). Ice of the Superior lobe was sourced from eastern Canada and advanced along the axis of the deep western basin of Lake Superior (Mooers and Lehr, 1997). The oldest well-defined limit of the Superior lobe is the St. Croix moraine, a large, lobate moraine that formed in conjunction with the Rainy lobe (Wright et al., 1973). An older advance correlated to the Emerald phase in Wisconsin likely created a set of low-relief morainic features 10–15 km in front of the St. Croix limit (Johnson, 2000). Superior lobe sediments are distinguished by a striking red color created by erosion of red-bed sandstones and mafic igneous bedrock underlying the Lake Superior basin associated with the ca. 1.1 Ga Midcontinent rift.

Figure 1.

Generalized pattern of late Wisconsin glaciations, with emphasis on the Superior lobe readvances. The figure is adapted from Wright (1972) and Patterson and Johnson (2004).

Figure 1.

Generalized pattern of late Wisconsin glaciations, with emphasis on the Superior lobe readvances. The figure is adapted from Wright (1972) and Patterson and Johnson (2004).

Multiple readvances punctuated ice retreat from the St. Croix moraine (Fig. 1) (Wright, 1972; Wright et al., 1973; Johnson and Mooers, 1998). Two post–St. Croix readvances created discernable end moraines: the Automba readvance, which created the Mille Lacs moraine system, and the Nickerson readvance, which created the Thomson and Nickerson moraines. A third readvance, named the Split Rock, occurred between the Automba and Nickerson phases. The Split Rock lacks an end moraine except very locally, and instead the limit is defined by the terminations of subglacial stream deposits. Determining the extent of retreat prior to each readvance is challenging, but there are multiple till sheets enriched in silt and clay upsection. The hypothesis is that successive readvances overrode clay-rich glaciolacustrine sediments from proglacial lakes that formed after the ice front retreated to positions within the Lake Superior drainage basin (Wright et al., 1973).

The oldest till observable on this trip is part of the Cromwell Formation (Wright et al., 1970), which is associated with the St. Croix and Automba phases (Fig. 2). This till lacks the inclusion of overridden lacustrine clay. Cromwell Formation till is rocky, gravelly, and reddish-brown (5YR 4/4). The matrix texture is typically a loam to sandy loam, with an overall increase in sand from the Superior basin to the St. Croix moraine (Fig. 2). It is non- to slightly calcareous and deeply leached where exposed at the surface. Cromwell Formation till is visible at Stops 2-1, 2-8, and 4-1.

The Barnum Formation overlies the Cromwell Formation (Wright et al., 1970) (Fig. 2). Hobbs (2002, 2003a, b, 2004b), and Knaeble and Hobbs (2009), recognized three texturally distinct tills within the Barnum Formation, which are overlain and separated in places by reddish lake and deltaic sediment. They named three tills and one unit of lake sediment as informal members of the Barnum Formation.

From oldest to youngest the three distinct tills are: the Mahtowa member (called Lakewood member in the cited references), the Moose Lake member, and the Knife River member (Fig. 2). Each till is finer-grained overall than the preceding one, although there is significant overlap in the distribution of till textures. They are all reddish-brown in color (5–2.5YR 5/3–3/4), but the Moose Lake and Knife River members tend to be slightly more reddish (2.5 YR). The Mahtowa member is noncalcareous, whereas the upper members are calcareous. Clasts are uncommon in all members, but especially in the youngest (Knife River member).

Each of these tills has been correlated with a readvance. The Mahtowa member is correlated with the Split Rock readvance. This advance extended well out of the Superior basin, deep into Pine County where the till texture is not exactly the same, but till behind a set of proposed ice limits for the Split Rock advance is finer-grained than that of the earlier phases (Patterson, 2001). The Mahtowa member is exposed at Stops 2-8, 4-2, and 4-3. The Moose Lake member is correlated to the Nickerson readvance, and is exposed at Stops 2-3, 2-8, 2-9, 4-1, 4-2, and 4-3. The Knife River member may correlate to an equivalent of the “Marquette readvance” recognized in the eastern Upper Peninsula of Michigan (Drexler et al., 1983; Lowell et al., 1999). The ice associated with the Marquette readvance is part of the Green Bay or Michigan lobe, which flowed south from the eastern Superior basin. In northern Wisconsin, till belonging to the Douglas Member of the Miller Creek Formation, has been associated with the Marquette readvance, which is named the Lake View readvance in Wisconsin (Clayton, 1984). We consider the association of the Knife River member (and Douglas Member) with the Marquette readvance contentious. This subject is addressed below in the section titled “The Enigmatic ‘Marquette’ Readvance.”

In addition to the tills, Wright et al. (1970) mapped laminated red and gray lacustrine silt and clay varves in the Nemadji lake plain as the Wrenshall Formation. It is stratigraphically above the Moose Lake member, and up ice from the Thomson moraine. Knaeble and Hobbs (2009) define the Wrenshall Formation as a member of the Barnum Formation, because it is part of the same stratigraphic package of lake-influenced tills. This member is exposed at Stops 2-3 and 2-9.

Chronology of the Superior Lobe (St. Croix through Nickerson Phases)

Readvances of the Superior lobe are not well dated. Most radiocarbon dates used to constrain ice margins are from kettle lakes, and the process of melting ice blocks to form kettles often lags the retreat of the ice margin by thousands of years (Wright, 1976). In addition, many radiocarbon dates from basal lake sediments are from bulk organic carbon, which often includes carbon from aquatic plants derived from dissolved 14C-free carbonate rock rather than the atmosphere (Deevey and Stuiver, 1964). This results in radiocarbon dates that are much older than the associated sediment.

Multiple radiocarbon dates from a site near Wolf Creek within the St. Croix limit suggest that the St. Croix moraine is older than 16.0 14C ka B.P. (Birks, 1976; Clayton and Moran, 1982; Mooers and Lehr, 1997). The ages of the younger Superior lobe readvances are poorly constrained, but the area inside the Vermilion moraine was deglaciated by ca. 12.0 14C ka B.P. (Florin and Wright, 1969; Björck, 1990; Lowell et al., 2009). These dates, which are from macrofossils and not sourced from kettle lakes, do not compare favorably with the radiocarbon dates from kettles associated with the Automba and Split Rock phases. These include basal dates from 16.0 to 15.0 14C ka B.P. from kettle lakes Kotiranta and White Lily, that have been associated with the Split Rock phase (Wright and Watts, 1969; Wright et al., 1973), and a basal date from Cloquet Lake on the Highland moraine of ca. 16.5 14C ka B.P. (Hill, 2007).

Basal radiocarbon dates from kettles lakes on the Nickerson phase Thomson moraine are ca. 12.0 14C ka B.P., but two peat samples within meltwater channels associated with the Thomson moraine date to ca. 10.5 14C ka B.P. (Wasylikowa and Wright, 1970; Wright et al., 1973). This younger date is similar to that of the Steep Rock moraine of the Rainy lobe (Fig. 3), which was deglaciated by ca. 10.4 14C ka B.P. (Lowell et al., 2009). Related to the Split Rock and Nickerson phases is an extensive set of ice marginal channels that go around, and cut through the moraines (Knaeble and Hobbs, 2009). The channels carried meltwater from the St. Louis sublobe, which retreated to form glacial Lake Aitkin–Upham (Figs. 1 and 3) (Hobbs, 1983). The youngest advance of the St. Louis sublobe pre-dates the Vermilion moraine (Marlow et al., 2004; Mooers et al., 2005). Stops 2-1, 2-3, 2-4, 4-2, and 4-3 all include evidence for drainage of the Lake Aitkin–Upham basin, both during and after the Nickerson readvance.

Figure 2.

Till textures of the Cromwell and Barnum Formations and idealized stratigraphy. Data compiled from data on file at the Minnesota Geological Survey.

Figure 2.

Till textures of the Cromwell and Barnum Formations and idealized stratigraphy. Data compiled from data on file at the Minnesota Geological Survey.

Figure 3.

Summary of Lake Superior basin ice margins and chronology (ages in 14C ka B.P.). Dates on the moraines in Ontario are from Lowell et al. (2009). The Grand Marais margin is dated by the Gribben Forest Bed (Lowell et al., 1999). The 10.0 14C ka B.P. dates from the „red clay till“ in Wisconsin and Michigan are from Hack (1965) and Black (1976).

Figure 3.

Summary of Lake Superior basin ice margins and chronology (ages in 14C ka B.P.). Dates on the moraines in Ontario are from Lowell et al. (2009). The Grand Marais margin is dated by the Gribben Forest Bed (Lowell et al., 1999). The 10.0 14C ka B.P. dates from the „red clay till“ in Wisconsin and Michigan are from Hack (1965) and Black (1976).

Glacial Lakes of the Superior Lobe

Retreat of the Superior lobe into the Superior basin created proglacial lakes. Small, ice marginal lakes formed initially, but these lakes coalesced to form a larger lake. The glacial lake confined to the western Superior basin is named glacial Lake Duluth. The name can be confusing, because multiple lake levels are identified for glacial Lake Duluth, but the most prominent is named the Duluth level. There are also “epi-Duluth” levels above the Duluth level, during which glacial Lake Duluth, and a smaller precursor named Lake Nemadji, drained through the Moose Lake (Portage) outlet into the Kettle River. Ice retreat opened the lower Brule outlet into the St. Croix River (Figs. 1 and 3) and established the Duluth level. Ice retreat from the Keeweenaw Peninsula opened lower eastern outlets, and the lake dropped to “post-Duluth” levels. The first eastern outlets were ice marginal channels that drained across the Upper Peninsula of Michigan to the Lake Michigan basin via the Au Train–Whitefish channel (Fig. 3). Continued ice retreat opened a lower outlet to the Lake Huron basin via the St. Mary’s River (Fig. 3). At this stage, glacial Lake Duluth coalesced with a separate proglacial lake in the eastern basin named glacial Lake Minong. Progressive downcutting of a drift-covered sill at the St. Mary’s river caused falling lake levels in Lake Minong.

The lake level history outlined above was established by Far-rand (1960), but has since been complicated by the recognition of the ca. 10.0 14C ka B.P. Marquette readvance in the eastern basin (Fig. 3) (Drexler et al., 1983; Lowell et al., 1999). In their review, Farrand and Drexler (1985) speculated that the Superior lobe also readvanced into the western basin, but did not completely overrun glacial Lake Duluth, so that that the youngest phase of the Duluth level was contemporaneous with the Marquette advance in Michigan. This view is somewhat different than Clayton (1984), who suggested that the Duluth level dates to ca. 9.5 14C ka B.P., and that the Marquette readvance overran the entire western Superior basin.

New radiocarbon dates on the Lake Duluth level are consistent with Clayton’s (1984) view that the Duluth level and the highest Lake Minong level are separated by very little time. Wood from basal sand within the Moose Lake outlet dates to 9360 ± 70 14C yr B.P. (Beta-61766) (Bacig and Huber, 1993; H. Mooers, 2010, personal commun.). Wood within basal sediments from Lake St. Croix within the Brule spillway dates to 9420 ± 75 14C yr B.P. (ETH-31000) (T. Lowell, 2008, personal commun.). A date from Lily Lake on Isle Royale suggests lake levels had fallen from the Duluth level prior to 9420 ± 90 14C yr B.P. (AA-12529) (Flakne, 2003).

These dates, which are all ca. 9.4 14C ka B.P., are intriguing because Lake Agassiz overflow diverted into the Lake Superior basin at this time. Lake Agassiz was a massive proglacial lake that was confined initially to the Red River valley of the Dakotas, Minnesota, and Manitoba, but expanded northward with ice retreat. The history of Lake Agassiz is complex, but ca. 9.4 14C ka B.P., levels in Lake Agassiz fell due to the diversion of overflow into the Lake Superior basin (Teller and Thorleifson, 1983; Fisher, 2003). The coeval dates from the Brule and Moose Lake spillways raise the possibility that the diversion of Lake Agassiz overflow into the Lake Superior basin was into glacial Lake Duluth, rather than the younger lake, glacial Lake Minong, which overflowed into the Lake Huron basin. The volume of water from Lake Agassiz that spilled into the Superior basin due to drawdown of Lake Agassiz is estimated to have been 7000 km3 (Teller et al., 2002), which is nearly as great as our estimated volume for glacial Lake Duluth (9200 km3).

For this field guide, we have mapped the Duluth level strandline in an attempt to clarify the spatial extent, because the elevation data of Farrand (1960) is too scattered to substantiate a continuous strandline. Using shaded relief and slope maps of the western Superior basin generated from 10-m digital elevation models (DEMs) (Gesch, 2007), the Duluth strandline was traced using ArcGIS. After tracing the base of identifiable terraces, elevation data were extracted from the DEMs to create an isobase map (isobases are lines of equal uplift), a paleogeographic map, and a plot of elevation versus distance perpendicular to the isobases (Fig. 4). The Brule outlet was the main outlet for the Duluth level, but the Moose Lake outlet was likely active as well during periods of extreme discharges (c.f. Carney, 1996).

The Enigmatic “Marquette” Readvance

At the same time as the Marquette readvance in Michigan, there was a readvance of the Superior lobe in Thunder Bay (Ontario, Canada) to the Marks moraine (Fig. 3) (Loope, 2006). There is no evidence to suggest either the Marquette advance to the Grand Marais moraine in Michigan, nor the advance to the Marks moraine was more than several tens of km, but the ice advance in the western Superior basin is typically depicted as a 250-km advance that completely filled glacial Lake Duluth with ice (e.g., Clayton, 1983; Farrand and Drexler, 1985; Dyke, 2004). A massive red clay in the western Superior basin, designated here the Knife River member, has been associated with this readvance (Clayton, 1984; Hobbs, 2004a; Mooers et al., 2005). The strongest evidence for this readvance in the western Superior basin are four radiocarbon dates on spruce and hemlock wood in “red clayey till,” near the border of Wisconsin and Michigan that date to 10.0 14C ka B.P. (Fig. 3) (Hack, 1965; Black, 1976).

The potential for an extensive readvance of the Superior lobe in the western Superior basin is curious because the great depth of the basin is hypothesized to have caused large losses of ice from calving and inhibit ice advance (Cutler et al., 2001). There are also three submerged moraines between the Keeweenaw Peninsula and Isle Royale that rise to over 50 m above the modern lake bed that have not been correlated to moraines on land (Landmesser and Johnson, 1982). These moraines would correlate well with the Marks and Grand Marais moraines in the eastern Upper Peninsula, but this would require that the Superior lobe did not readvance very far (if at all) into southwestern Lake Superior (Fig. 3).

The most controversial aspect of the Marquette readvance is the potential impact the ice margin had on Lake Agassiz drainage during the Younger Dryas, a globally recognized climatic cooling event that lasted between ca. 11.0–10.0 14C ka B.P. For many years, the leading hypothesis to explain the Younger Dryas was a shift in drainage of Lake Agassiz from a southern outlet into the Mississippi River basin, to an eastern outlet into the Superior basin. This drainage shift could flood the North Atlantic Ocean with freshwater, and disrupt thermohaline circulation, precipitating climatic cooling (Broecker et al., 1989). This hypothesis supposes that the Superior lobe had retreated far enough to allow Lake Agassiz to overflow into the Superior basin by ca. 11.0 14C ka B.P. Theoretically, the Marks readvance blocked eastern Lake Agassiz overflow. New studies have challenged this idea. One argument is that the Rainy lobe never retreated far enough north to allow eastern Lake Agassiz drainage into the Superior basin by the onset of the Younger Dryas (e.g., Lowell et al., 2005).

There is excellent exposure of the Knife River member at Stops 2-4 and 2-9. Similar to descriptions along the southern shore of Lake Superior in Wisconsin, the unit is right at the surface, and within the weathered soil profile. Usually absent is glaciolacustrine clay or silt associated with glacial Lake Duluth. Perhaps there would have been non-depositional zones in Lake Duluth at shallow water depths, or on significant slopes, but the absence of glaciolacustrine sediment above the massive red clay occurs even on the low slopes along the modern lakeshore, which would be over 400 ft (122 m) below the Duluth level (Clayton, 1984; Hobbs, 2004a).

Alternatively, the Knife River and Douglas Members may not be till, but glaciolacustrine sediment associated with glacial Lake Duluth. The sediment may have been remobilized by slumping following lake-level drawdown. The boulders could be ice-rafted debris, and freeze-thaw processes after subaerial exposure may have concentrated the boulders on the surface. If this is the case, there may not be till in the southwestern basin associated with a Marquette-age readvance. Perhaps the “red clayey till” from which the 10.0 14C ka B.P. radiocarbon dates along the Michigan-Wisconsin border derive is actually lacustrine sediment (Hack, 1965; Black, 1976). The radiocarbon dated localities are all below the Duluth-level strandline. A minor readvance of the Superior lobe may have been enough to block outlets across the Upper Peninsula and raise lake levels, which would have flooded forested lowlands and caused widespread slumping. We hope the selected exposures of the Knife River member promote discussion on whether or not the regional red clay that occurs at, or right near, the surface is evidence of a late readvance (perhaps the regional Marquette equivalent), or glaciolacustrine sediment deposited in glacial Lake Duluth (and perhaps reworked following lake drawdown).

Figure 4.

Glacial Lake Duluth paleogeography, isobases, and elevation data determined from 10-m Digital Elevation Models from the National Elevation Data set (Gesch, 2007). asl—above sea level.

Figure 4.

Glacial Lake Duluth paleogeography, isobases, and elevation data determined from 10-m Digital Elevation Models from the National Elevation Data set (Gesch, 2007). asl—above sea level.

ROAD LOG—DAY 1

Assemble at the parking lot of the Holiday Inn Express Hotel and Suites at the Minneapolis Convention Center in Minneapolis. The road log begins on I-35W at the interchange with I-94.

MileageDirections
0Merge onto I-35W northbound near the interchange with I-94 in Minneapolis.
25Continue north on I-35 (which merges with I-35E). This is mile marker #127 of I-35W.
133.2Take the Carlton exit #235, then turn left (west) onto MN-210 to the Black Bear Resort and Casino and turn right (north) to enter the Black Bear Resort and Casino.
MileageDirections
0Merge onto I-35W northbound near the interchange with I-94 in Minneapolis.
25Continue north on I-35 (which merges with I-35E). This is mile marker #127 of I-35W.
133.2Take the Carlton exit #235, then turn left (west) onto MN-210 to the Black Bear Resort and Casino and turn right (north) to enter the Black Bear Resort and Casino.

I-35N Highlights

  • Between mile marker #127 and #165, I-35 crosses the Anoka sand plain, the floor of glacial Lake Anoka, which developed with the downwasting of the Grantsburg sublobe of the Des Moines lobe. The hill after exit #165 is the Pine City moraine, the end moraine of the Grantsburg sublobe (Figs. 1 and 5).

  • Beginning at mile marker #309 and continuing to Black Bear Resort, I-35 crosses Nickerson-phase outwash and moraine deposits (Fig. 5). The moraine complex was bisected by the half-mile-wide Moose Lake spillway, now occupied by the Portage River, right before mile marker #216 (Fig. 5). The Lake Superior drainage divide is ∼5 km northeast of I-35.

  • After the Barnum exit (#220), I-35 tracks in and out of the meltwater channels from the St. Louis sublobe and Aitkin-Upham basin, which were diverted around ice of the Thomson moraine (Fig. 5). The Black Bear Casino sits in one of these wide channels.

  • End Day 1.

ROAD LOG—DAY 2

MileageDirections
00.7Turn left heading east onto MN-210 toward Carlton, Minnesota.Turn right (south) onto 3rd Street/County Road 1.
3.1Turn right into the driveway for the Schaefler and sons gravel pit (private property).
MileageDirections
00.7Turn left heading east onto MN-210 toward Carlton, Minnesota.Turn right (south) onto 3rd Street/County Road 1.
3.1Turn right into the driveway for the Schaefler and sons gravel pit (private property).

Stop 2-1. Epi-Duluth (Lake Nemadji?) Delta (15T, 545900 E, 5164900 N)

During the earliest stages, the Lake Superior basin received meltwater from the St. Louis River, which drained the St. Louis sublobe and glacial Lake Aitkin-Upham (Hobbs, 1983; Knaeble and Hobbs, 2009). As long as ice filled the lake basin, this drainage was diverted around the ice lobe in a series of channels (Fig. 5). As the ice melted back from the Nickerson ice margin, a small lake was created, draining through the Moose Lake (Portage) outlet at a high level. Small wave-planed surfaces up to 1150 ft (351 m) in elevation are attributed to this early lake.

Little evidence remains of this early lake, nor has it been named. But some of the meltwater coming down the St. Louis River built a high-level delta here. Its apex on the north side rises to 1160 ft (354 m), declining south to ∼1140 ft (347 m) over a half mile. It was presumably bounded on the northwest, west, and southwest sides by ice, where the flat delta top gives way to stagnant ice topography. Only the western part of the delta is preserved. On the northeast, east, and southeast sides, the delta has been truncated by a scarp cut by water flows down the St. Louis River into a lower stage of Lake Duluth. As the ice margin retreated, the lake grew and coalesced into a lake with a local surface at ∼1100 ft (335 m), or ∼40 ft (12 m) above the Duluth level, named Lake Nemadji by Leverett (1932). Subsequent ice retreat and channel incision at the Moose and Brule outlets dropped levels farther.

The pit is ∼50 ft (15 m) deep at maximum. The haul road down the east side gives access to the west-facing wall of the pit, which exposes well-sorted coarse sand and fine gravel in large crossbeds dipping south. Few if any large rocks are visible. These beds are interpreted as foreset beds of a delta built into a high-level lake, whose surface was ∼100 ft (30 m) above the Duluth level (Fig. 4). A sample of till from the floor of the pit was obtained with the help of a friendly loader operator. The (gravel) sand-silt-clay ratio tested to be (1) 49-37-14, typical of the Cromwell Formation (Fig. 2) (The (1) 49-37-14 notation indicates that the sample is 1% gravel by weight. The remaining non-gravel matrix is normalized to 100% to conveniently plot on a ternary diagram.) (Described by H.C. Hobbs in 2006.)

Mileage3.1DirectionsTake a right turn (south) onto County Road 1.
6.4Turn right (west) onto County Road 4/Military Road. (The Duluth strandline is ascended on this stretch.)
10.5Turn left (south) onto County Road 103. (The Duluth strandline is descended on this stretch.)
13.6Turn right (west) onto Baker Road (after going down and up the Blackhoof River valley). (The Duluth strandline is readily visible on the right side of the road as we pass the Baker farm.)
14.7Turn left on County Road 104, which turns intoCounty Road 105 after a mandatory right turn.
15.9Turn left (south) onto Pioneer Road.
17Pull over onto the roadside to inspect a borrow pit in the Duluth level wave-cut terrace (private property).
Mileage3.1DirectionsTake a right turn (south) onto County Road 1.
6.4Turn right (west) onto County Road 4/Military Road. (The Duluth strandline is ascended on this stretch.)
10.5Turn left (south) onto County Road 103. (The Duluth strandline is descended on this stretch.)
13.6Turn right (west) onto Baker Road (after going down and up the Blackhoof River valley). (The Duluth strandline is readily visible on the right side of the road as we pass the Baker farm.)
14.7Turn left on County Road 104, which turns intoCounty Road 105 after a mandatory right turn.
15.9Turn left (south) onto Pioneer Road.
17Pull over onto the roadside to inspect a borrow pit in the Duluth level wave-cut terrace (private property).
Figure 5.

Overview of stops for Days 2 and 4. Areas of presumably thicker drift with hummocky topography are shaded white. The other mapped glacial landforms are: lineated bedforms (white), eskers (gray), single ridge end moraines (dashed black and gray) and meltwater and glacial-lake overflow channels (black).

Figure 5.

Overview of stops for Days 2 and 4. Areas of presumably thicker drift with hummocky topography are shaded white. The other mapped glacial landforms are: lineated bedforms (white), eskers (gray), single ridge end moraines (dashed black and gray) and meltwater and glacial-lake overflow channels (black).

Stop 2-2. Borrow Pit along the Duluth Level Strandline (15T, 537650 E, 5153340 N)

This borrow pit is dug into the backslope of a wave-cut scarp at the Duluth level (Figs. 4 and 5). The break in slope in this area is between 1150 and 1160 ft (350 and 354 m) above sea level (asl). This scarp is relatively continuous in the lake plain of Carlton County (Minnesota) and adjacent Douglas County (Wisconsin). It is generally cut into lake sand of the Nemadji phase, which, in turn, is reworked sediment from the Nickerson advance.

When originally described in 2007, the borrow pit exposed fine unbedded sand containing a few pebbles and larger rocks. It has since been cut back to reveal some clay of uncertain origin within the sand. Considering the erodible material that makes up the scarp, only a short period of erosion was probably necessary. This presumably represents the final occupation of the Duluth level. If they existed, older Duluth levels would have been slightly below this level, and would have been obliterated by a slowly transgressing shoreline caused by uplift of the Brule outlet at rates faster than this part of the basin.

MileageDirections
17Continue south on Pioneer Road.
17.9At the end of Pioneer Road, take a left turn (east) onto Spring Lake Road/County Road 6. Spring Lake Road doglegs left after 2.4 mi, then right after 1.8 mi.
22.1Do not veer to the left, but continue straight to stay on the gravel Spring Lake Road.
24.1Turn right (south) onto County Road 1.
24.3Turn right on MN-23.
24.8Park on the shoulder above the Deer Creek culvert to inspect the exposed clay bank on the east side of the road in the creek valley.
MileageDirections
17Continue south on Pioneer Road.
17.9At the end of Pioneer Road, take a left turn (east) onto Spring Lake Road/County Road 6. Spring Lake Road doglegs left after 2.4 mi, then right after 1.8 mi.
22.1Do not veer to the left, but continue straight to stay on the gravel Spring Lake Road.
24.1Turn right (south) onto County Road 1.
24.3Turn right on MN-23.
24.8Park on the shoulder above the Deer Creek culvert to inspect the exposed clay bank on the east side of the road in the creek valley.

Stop 2-3. Red-Gray Varves (Wrenshall Member) above Till (Moose Lake Member), MN-23 and Deer Creek (15T, 546950 E, 5152490 N)

The exposed lake bottom of glacial Lake Duluth forms a wide shelf in Carlton and Douglas Counties that gently slopes from above the Duluth level to the modern level of Lake Superior. The lake plain is heavily dissected by the Nemadji River and its tributaries. The soft lake sediment is easily eroded, and the major streams have cut through the entire glacial lake section, into the underlying Moose Lake till. Despite the deep dissection, good exposures are rare. The valleys are heavily forested and slumping is ubiquitous. The clay will not form steep stable cuts, but the slumping does expose small, shortlived scarps. These, plus some power auger borings, provide a glimpse of the sediments.

Fine sand deposited in shallow water typifies the surface at elevations above 1000 ft (305 m). Below this level, the surface is generally clayey, and sometimes appears as varves (Zarth, 1977). This stop highlights a varve site along the lower slope of the Deer Creek valley. The slumping has been triggered by enhanced erosion downstream from a culvert under Minnesota Highway 23. The undissected lake plain above is ∼900 ft (274 m), or 150 ft (46 m) below the Duluth level, and the bottom is ∼800 ft (244 m), giving a total 100 ft (30 m) of lake sediment since the Nickerson phase. The surface soil on these valley sides is soft uniform clay, 2.5YR 4/3-3/4, with very strong fine to very fine angular blocky structure. It is oxidized and has been subject to many wet-dry cycles. It has presumably crept and slumped from higher on the hillside. This material was not defined in a soil series, but is mapped “udorthents” on these slopes (Lewis, 1978).

Under the surface colluvium, the rhythmically bedded clay is unoxidized, with alternating “red” and gray laminae. The red beds are 5YR 5/2; the gray beds are generally 2.5Y 4-5/1. Some beds are transitional between the two end members. Both beds are calcareous, but the gray more so than the red. The gray beds break along horizontal planes which appear to be very thin, calcareous, coarse silt beds. The red beds are uniform, and break with conchoidal fracture. (Section described by H.C. Hobbs in 2006.) One texture sample was taken of each. The sand-silt-clay ratio of the gray sample is 0-61-39, (silty clay loam); the ratio of the red sample is 0-19-81 (clay).

Are these beds varves? And why the color alternation? The regular alternation of textures is consistent with winter (red)-summer (gray) deposition. This difference is explained by different sources, with distinct grain-size differences. The site is only ∼10 mi from the St. Louis River inlet to the lake, and a similar distance from an earlier channel inlet. Both of these inlets supplied western-source water and sediment from glacial Lake Aitkin-Upham, and perhaps Lake Koochiching (eastern Lake Agassiz). Inputs of red sand, silt and clay from the melting Superior lobe may have been much more distant, resulting in suspension settling of fine lake clay during the ice covered months.

MileageDirections
24.8Turn around to backtrack north on MN-23.
31.0Turn right (east) onto County Road 4/MilitaryRoad.
32.9Turn left (north) onto the BNSF access road (permission is necessary to access).
33.7Park in a clearing and walk 0.2 mi to a gully on the east side of the railway.
MileageDirections
24.8Turn around to backtrack north on MN-23.
31.0Turn right (east) onto County Road 4/MilitaryRoad.
32.9Turn left (north) onto the BNSF access road (permission is necessary to access).
33.7Park in a clearing and walk 0.2 mi to a gully on the east side of the railway.

Stop 2-4. Red Clay (Knife River Member) over Delta Sand, Fond du Lac State Forest (15T, 554130 E, 5161870 N)

This gully section was originally discovered by Howard Mooers (Mooers et al., 2005), and has been shown on several field trips (Marlow et al., 2004). It displays the massive red clay of the Knife River member of the Barnum Formation over a deposit of clean, fine sand.

The upper unit is red clay interbedded with very fine yellowish sand. The pure clay is as red as 10R 4/3 (weak red); the silty clay portion is 7.5YR 4/3 (brown). The sand is light yellowish brown (2.5Y 6/3). The clay is moderately calcareous. The sand is highly calcareous. The beds are highly distorted, and cannot be traced from one side of the cut to the other. The clay is greatly cracked by wetting and drying. To the south of the described cut, the beds are even more distorted and contain pebbles and cobbles. Only ∼1.2 m of this upper unit is exposed, but the top of the gully is ∼5 m below the ballast of the adjacent BNSF railway, and red clay is exposed through thin soil on the slope between.

The lower unit is mostly very fine sand–coarse silt, like the sand beds in the upper unit. It is generally pale yellow (2.5Y 7/4), but includes thin medium silt beds, which are moister and darker (light yellowish brown, 2.5Y 6/3). Some bands of very fine sand are slightly redder. Bedding is generally flat but wavy, and includes ripple cross-bedding in one zone. This unit is sporadically exposed along the side of the gully to where it joins a larger valley, ∼9 m below the rim of the gully (described by H.C. Hobbs in 2007).

Is the red clay here a till? And if so, does it correlate with other red clay sections that have been interpreted as till, and was it deposited by the Marquette advance?

MileageDirections
33.7Turn around and head south back to County Road 4/Military Road.
34.8Turn right (west) onto County Road 4/Military Road.
36.8Turn right (north) onto MN-23. Continue to West Duluth.
52.0Turn left (north) onto N 59th Avenue W in the city of West Duluth.
52.8Turn left (west) onto Highland Street.
53.1Take the first right (north) onto N 64th Avenue W into the Oneota Cemetary.
MileageDirections
33.7Turn around and head south back to County Road 4/Military Road.
34.8Turn right (west) onto County Road 4/Military Road.
36.8Turn right (north) onto MN-23. Continue to West Duluth.
52.0Turn left (north) onto N 59th Avenue W in the city of West Duluth.
52.8Turn left (west) onto Highland Street.
53.1Take the first right (north) onto N 64th Avenue W into the Oneota Cemetary.

Stop 2-5. Duluth Level Terrace, Oneota Cemetary, West Duluth (15T, 562490 E, 5177870 N)

The best developed strandline in the western Lake Superior basin above the modern level is the Duluth level (Fig. 4). The strandline is particularly conspicuous along the southern shore of Lake Superior, where it usually appears as a wave-cut terrace (generally eroded into ice-contact outwash or till), with an associated wave-built platform and lower terrace (Fig. 6A). The name Lake Duluth originates from Leverett (1928) after a series of prominent gravel beaches in the city of Duluth described by early geologists. According to Schwartz (1949), the Duluth level is “followed in a general way by Skyline Parkway” (formerly known as Terrace Parkway). Construction of the road makes identification of the natural versus manmade terrace difficult to assess with certainty. One exception is at Oneota cemetery, where Farrand (1960) described “a prominent wave-cut bluff” at 1020 ft (311 m).

At this location (Figs. 6B and 6C), Skyline Parkway snakes around Keene Creek, leaving the cemetery undeveloped. There are two prominent terraces, an upper terrace with a base at ∼1070 ft (326 m), and a less defined lower terrace at ∼1020 ft (311 m). We interpret the base of the upper terrace as the Duluth level (Fig. 4). The lower terrace is likely a wave-built terrace (Fig. 6A). Skyline Parkway is visible from the cemetery, and is locally built upon the 1070 ft (326 m) terrace.

After tracing the Lake Duluth terrace throughout the Lake Superior basin and fitting a line to the strandline data (Fig. 4), the Duluth level can be projected everywhere in the basin. Figure 6C plots the elevation of Skyline Parkway and the projected Duluth level. Schwartz’s (1949) assessment that Skyline Parkway follows the Duluth level is accurate, although there are several stretches that track above and below the Duluth level. Notable locations along Skyline Parkway that are at the Duluth level include: the old Skyline Parkway terrace along the Spirit Mountain ski slope, the parking lot of the Enger Tower golf course, the Twin Ponds, the 1st United Methodist Coppertop church, and Heller Hall on the University of Minnesota campus where the Department of Geological Sciences is housed.

MileageDirections
53.1Exit the cemetery by turning left (east) onto Highland Street.
53.9Turn right (south) onto N 59th Avenue W.
54.7Turn right (west) onto Grand Avenue/MN-23.
54.9Take a sharp left to merge onto I-35 northbound.
58.6Take Exit #256B for 5th Ave. W toward Lake Ave.
59.1Turn right onto Harbor Drive, then left at the stoplight onto W Commerce.
59.2Turn right (south) onto Lake Avenue S and continue over the Lift Bridge, and onto Minnesota Avenue.
63.4Park in the Park Point parking lot.
MileageDirections
53.1Exit the cemetery by turning left (east) onto Highland Street.
53.9Turn right (south) onto N 59th Avenue W.
54.7Turn right (west) onto Grand Avenue/MN-23.
54.9Take a sharp left to merge onto I-35 northbound.
58.6Take Exit #256B for 5th Ave. W toward Lake Ave.
59.1Turn right onto Harbor Drive, then left at the stoplight onto W Commerce.
59.2Turn right (south) onto Lake Avenue S and continue over the Lift Bridge, and onto Minnesota Avenue.
63.4Park in the Park Point parking lot.

Stop 2-6. Park Point (lunch) (15T, 572400 E, 5175700 N)

In combination with Wisconsin Point, Park Point (or Minnesota Point) is one of the longest freshwater baymouth beaches in the world. This beach has a classic profile, with well developed berms and backshore dunes, but there has been no formal study of the morphology, sedimentology, or geologic history of this island. In Duluth, lake levels are currently transgressing at a rate of 2.5 mm/yr (Mainville and Craymer, 2005), but climatic variability has caused water levels to vary by 1.2 m over the past 150 years. Transgressing shorelines erode and redeposit shallow-water sand along the advancing waterfront, which creates a steady supply of sand. If the sand supply is large enough, the shoreface will grow vertically as levels rise (e.g., Johnston et al., 2007). Park Point receives sand from western longshore drift along the northern and southern shores, although the supply of sand should be much greater from the southern shore due to the easily eroded bluffs of Bayfield sandstone and till along the Wisconsin shore (Matheson and Munawar, 1978; Kemp et al., 1978).

The large beach may owe some of its existence to the Nipissing transgression, which culminated between 6000 and 4500 years ago (Larsen, 1985; Thompson and Baedke, 1997). The Nipissing transgression was caused by uplift of the North Bay outlet into the Ottawa River when lake levels were confluent in the Michigan, Huron, and Superior basins. Uplift of the North Bay outlet created rising lake levels in most of Lake Superior, as well as within the Lake Huron and Michigan basins, which created well-developed beach ridges throughout the upper Great Lakes (Larsen, 1985). The Nipissing strandline projects to the modern lake level in the Duluth area, but rises in elevation to the northeast. On Day 3, the drive along Highway 61 north of Grand Marais is along a shingle beach associated with the Nipissing transgression.

MileageDirections
59.2Head back north on Minnesota Avenue toward Duluth.
62.5Do not veer right onto Lake Avenue, but continue north on Minnesota Avenue.
62.8Park outside the gates to the U.S. Army Corps of Engineers dock.
MileageDirections
59.2Head back north on Minnesota Avenue toward Duluth.
62.5Do not veer right onto Lake Avenue, but continue north on Minnesota Avenue.
62.8Park outside the gates to the U.S. Army Corps of Engineers dock.
Figure 6.

Summary of the Duluth level along Skyline Parkway in Duluth, Minnesota. (A) is modified from Clayton (1984). (B) is a Google Earth screen capture of the Oneota Cemetery in Duluth. (C) is original data of the Lake Duluth terrace extracted from 10-m National Elevation Dataset digital elevation models.

Figure 6.

Summary of the Duluth level along Skyline Parkway in Duluth, Minnesota. (A) is modified from Clayton (1984). (B) is a Google Earth screen capture of the Oneota Cemetery in Duluth. (C) is original data of the Lake Duluth terrace extracted from 10-m National Elevation Dataset digital elevation models.

Stop 2-7. RV Blue Heron Tour and Inspection of Glacial Varves from Lake Superior (15T, 569200 E, 5180530 N)

The RV Blue Heron is part of the fleet of University National Oceanographic System (UNOLS) vessels and operated by the Large Lakes Observatory at the University of Minnesota Duluth as a charter vessel for research scientists. The vessel was built in 1985 for fishing the Grand Banks, but was sold to the University of Minnesota and converted for research in 1998. Over the past 14 years, multiple studies have utilized the geophysical and sediment coring equipment aboard the Blue Heron for extending our knowledge about the Quaternary history of the Lake Superior basin. Equipment includes acoustic seismic profilers that operate on a range of frequencies for imaging both shallow and deep sediments, and a piston corer capable of recovering sediment cores up to 9 m in length.

At this stop, we can examine sections from two Lake Superior sediment cores on loan from the National Lacustrine Core Repository in Minneapolis, cores BH02-5P and LS00-3P. BH02-5P is from the deep Caribou sub-basin of Lake Superior, east of the Keeweenaw peninsula (Fig. 3). BH02-5P has been correlated with photographs from S62-8, a long gravity core that penetrated to bedrock. By combining these records, 1406 varves have been measured that overlie a red till and sandstone. The record dates to between 9.3 and 8.1 14C ka B.P. The most intriguing aspect of this record is a series of ∼36 anomalously thick varves that correlate with those from the northern Lake Superior sub-basins. These varves are at the very top of the record, when the ice margin was most distal, and must have resulted from anomalously high sediment and water fluxes into the Superior basin (Breckenridge et al., 2004; Breckenridge, 2007).

LS00-3P is from western Lake Superior and includes three sets of varves that abruptly thicken, then thin. Because of their age (ca. 9.4 14C ka B.P.) and unusual pattern, they were hypothesized to have resulted from catastrophic flooding from Lake Agassiz when the Nipigon outlets first opened (Fig. 3). New geochemical data from split core X-ray fluorescence scans conducted at the Large Lakes Observatory support this idea. The thick varves have an anomalous geochemical signature, including higher vanadium:copper ratios (Fig. 7). Vanadium (as well as Mn) concentrations are higher in sediments from southern Lake Winnipeg, and believed to be associated with influx from rivers draining the prairies of central Canada. Copper (as well as Ni and Zn) is higher in sediments from northern Lake Winnipeg and is associated with rivers draining the Canadian Shield (Henderson, 1996). Lake Agassiz influx should have a geochemical signature that includes a western Canadian provenance, and V/Cu ratios have been proposed as a proxy to distinguish this western source (Breckenridge, 2005). Because of their high resolution and continuous stratigraphy, the study of varved sediments hold great promise for advancing our understanding of the paleohydraulic history of the Great Lakes.

MileageDirections
62.8Head northwest onto Minnesota Avenue. Take the first right, then the next left to get back onto S. Lake Avenue.
63.3Cross the Aerial Lift Bridge, and continue to head north on Lake Avenue.
63.8Turn right on W Commerce Street/W Lake Place.
63.9Turn left (north) onto N Lake Avenue, then take a right to merge onto I-35 northbound.
66.4Continue onto MN-61/London Road, and continue onto the MN-61 Expressway.
79.6Turn left (north) onto Homestead Road.
84.3Turn left (west) onto Clover Valley Road.
85.2Continue to the end of Clover Valley Road and enter the Peterson gravel pit (private property).
MileageDirections
62.8Head northwest onto Minnesota Avenue. Take the first right, then the next left to get back onto S. Lake Avenue.
63.3Cross the Aerial Lift Bridge, and continue to head north on Lake Avenue.
63.8Turn right on W Commerce Street/W Lake Place.
63.9Turn left (north) onto N Lake Avenue, then take a right to merge onto I-35 northbound.
66.4Continue onto MN-61/London Road, and continue onto the MN-61 Expressway.
79.6Turn left (north) onto Homestead Road.
84.3Turn left (west) onto Clover Valley Road.
85.2Continue to the end of Clover Valley Road and enter the Peterson gravel pit (private property).
Figure 7.

Stratigraphic data from LS00-3P section 3, including: X-ray radiograph, varve thickness data, percent calcite from carbon coulometry, and scanning X-ray fluorescence V/Cu and V/Ti ratios. The original core description and varve thickness data is from Breckenridge (2007). The red, massive layer is laminated in the X-ray radiographs. V/Cu ratios were proposed by Breckenridge (2005) to be a proxy for Lake Agassiz influx into Lake Superior (higher V = more Agassiz water and sediment).

Figure 7.

Stratigraphic data from LS00-3P section 3, including: X-ray radiograph, varve thickness data, percent calcite from carbon coulometry, and scanning X-ray fluorescence V/Cu and V/Ti ratios. The original core description and varve thickness data is from Breckenridge (2007). The red, massive layer is laminated in the X-ray radiographs. V/Cu ratios were proposed by Breckenridge (2005) to be a proxy for Lake Agassiz influx into Lake Superior (higher V = more Agassiz water and sediment).

Stop 2-8. Epi-Duluth Delta, Peterson Gravel Pit (15T, 586170 E, 5203770 N)

Features like this in the area east of Duluth were originally considered deltas into glacial Lake Duluth (Schwartz 1949, p. 72). However, they are much higher than the Duluth level viewed at Stops 2-2 and 2-5 (Fig. 4). They are also overlain by Cromwell till, and in some places by Mahtowa till.

The lower 3 m of sediment at this pit is poorly sorted gravel in a matrix of sand. It is crudely flat-bedded to unbed-ded, except one place shows a shallow dip to the west. Above this is a better sorted sand and fine gravel roughly 1.5 m thick, lacking large stones. Both deposits are non-calcareous. Nearly all of the clasts are dark and reddish fragments of bedrock from the Superior basin

The sand and gravel is capped by ∼3.7 m of very rocky till. It is non-calcareous, uniform, tough, and hard to dig. Its dominant color is reddish brown (2.5YR 4/4). It shows no visible incorporation of the underlying gravel. Matrix texture is borderline loam/sandy loam. Three texture samples of the till were run. From top to bottom, the (gravel) sand-silt-clay ratio was (19) 46-42-12, (17) 47-45-7, and (16) 47-46-7. The upper sample was from a layer described as less rocky and easier to dig, separated from the main body by a sharp wavy contact (described by H.C. Hobbs in 2002).

The upper till was initially interpreted as a layer of Mahtowa till, which is more silty and less rocky than the Cromwell till, but the difference in texture numbers at this site is underwhelming. However, other similar features in the area exhibit both Cromwell and Mahtowa till over stratified deposits.

If these till-capped gravel deposits are not beach deposits, what are they? They have a consistent elevation of ∼1180 ft (360 m), and could be deposits by meltwater streams that flowed at the edge of the Superior lobe as it shrank into the basin, hemmed in by higher ground to the northwest. These streams were on their way out of the basin, probably through the Moose Lake outlet. On their way, they encountered pockets of ponded water, and built little deltas into them, essentially filling them up. No visible strandlines can be related to these deltas, but some remnants of “side-hill” channels have been found in the topography at about the same level.

The ice then advanced to the Highland moraine, laying down a layer of till on the deltas but not destroying them. Another cycle of melting and readvance (Split Rock phase) led to the deposition of the silty Mahtowa till over some of them. The limit of the Mahtowa ice was barely high enough to cover the tops of the deltas.

MileageDirections
85.2Turn around and head back to MN-61 via Clover and Homestead roads.
90.0Turn left (northeast) onto MN-61.
93.6Turn left (north) onto Hawkhill Road.
MileageDirections
85.2Turn around and head back to MN-61 via Clover and Homestead roads.
90.0Turn left (northeast) onto MN-61.
93.6Turn left (north) onto Hawkhill Road.

Stop 2-9. Multiple Tills with Intervening Glaciolacustrine Sediment, Knife River Cutbank (15T, 392050 E, 5202600 N)

Active slumping along a 12-m-high cutbank of the Knife River exposes multiple tills, and two glaciolacustrine units (Fig. 2). The upper unit is glaciolacustrine, reddish brown (5 YR 4/3) clay, with ice-rafted clasts that vary from pebble to boulder in size. This unit is 1.2 m thick where observed, but it is not certain if the thickness is consistent across the cutbank. The unit is cracked by wetting and drying (and possibly freezing and thawing), making determination of possible bedding difficult, but in a fresh scarp, faint laminations were observed in wet clay that was sampled and allowed to dry. In addition to rocks, there are also rare clasts (from pebble to cobble size) of laminated reddish brown (5 YR 5/3) and pale red (2.5YR 6/2) silt. These clasts are believed to be ice rafted. The laminated silt is probably sourced from the freezing of lake sediment to basal ice following a readvance (Knight, 1997). Underlying the unit is a reddish brown (5 YR 4/3) sandy clayey loam, which is likely till. The texture is coarser than the unit above; the clasts are more abundant, and there is no hint of bedding.

The contact with this red till and the unit below is covered. Roughly halfway down the cutbank, there is a subtle break in slope that is the contact between a massive to laminated red (10YR 4/3) clay with few clasts, and a dark reddish gray (10R 4/1) sandy clayey loam with abundant clasts. This lower unit is harder, and forms a steeper slope. The red clay is interpreted as a second lacustrine unit, and the reddish gray loam is a second till. There is another break in slope ∼3 m above the river level that may represent an additional till, but the section is covered by slumped clay.

The upper unit is presumed to be the Knife River member, which may also include the reddish brown till below. This would suggest that the middle clay is the Wrenshall member that was deposited in a glacial lake prior to a readvance. The lower till may be the Moose Lake (?), but this designation is uncertain because the till is grayer and coarser than typical. Is the upper unit, the glaciolacustrine clay, the Knife River member? Is the till below this clay also the Knife River member or is this the Moose Lake member?

MileageDirections
94.7Turn around and head back to MN-61 via Hawkhill Road.
95.8Turn left (northeast) onto MN-61.
103.3Enter Two Harbors for dinner, then head northeast on MN-61 toward Grand Marais, Minnesota.
185.3Arrive at Hotel in Grand Marais.
Endof Day 2.
MileageDirections
94.7Turn around and head back to MN-61 via Hawkhill Road.
95.8Turn left (northeast) onto MN-61.
103.3Enter Two Harbors for dinner, then head northeast on MN-61 toward Grand Marais, Minnesota.
185.3Arrive at Hotel in Grand Marais.
Endof Day 2.

ROAD LOG—DAY 3

Refer to Dean and Phillips (this volume) for a description of the stops for Day 3.

ROAD LOG—DAY 4

MileageDirections
0Turn left and head south on MN-61.
106Turn left to merge onto I-35 southbound.
146Take Exit #220 (Barnum), and turn right (west) at the exit onto County Road 6/Main Street.
146.1Take the first right (north) on to County Road 140.
147.3Turn right into the borrow pit after Buck Road (private property).
MileageDirections
0Turn left and head south on MN-61.
106Turn left to merge onto I-35 southbound.
146Take Exit #220 (Barnum), and turn right (west) at the exit onto County Road 6/Main Street.
146.1Take the first right (north) on to County Road 140.
147.3Turn right into the borrow pit after Buck Road (private property).

Stop 4-1. Cromwell and Moose Lake Tills, Thomson Moraine, Supri Borrow Pit (15T, 524730 E, 5152170 N)

The lower 1.8 m of material is assigned to the Cromwell Formation. The reddish brown (2.5 YR 4/4) diamicton is non-calcareous, pebbly, rocky, sandy loam. It digs easily, which is somewhat unusual for Cromwell till. It exhibits platy structure in places, parallel to the exposure face. Within the diamicton are small sand inclusions, red clay clasts, and a few green crumbly cobbles and pebbles that appear to be grusified (disintegrating) gabbro.

Two samples were analyzed for texture and coarse-sand counting. The (gravel) sand-silt-clay ratio is (2) 61-26-16 and (4) 57-27-16, both sandy loam. Clast provenance is Superior; the ratios of light-dark-red grains in the 1–2 mm fraction are 33-28-29 and 36-31-33 (Hobbs, 1998). Almost all the grains are Precambrian; there are very few Paleozoic sandstone and chert grains.

The upper till, ∼2 m thick, is the Moose Lake member of the Barnum Formation. It is brown (7.5 YR 4/4) clay loam diamicton with fewer coarse clasts than the Cromwell. The color of the Moose Lake till is usually redder, whereas the underlying Cromwell is usually less red. The diamicton is uniform, noncalcareous, and also contains grusified gabbro pebbles. The Moose Lake unit exhibits strong medium angular blocky structure, especially in the upper part. There are black manganese oxide stains on many joint faces.

Analysis of two samples is as follows: (2) 33-40-28 and (1) 30-42-28, both clay loam. Clast provenance is Superior; almost all the 1–2 mm grains are Precambrian and the light-dark-red ratios are 28-36-36 and 31-27-43. Most of the red grains in both formations are red sandstone rather than red igneous.

The contact between the two tills is sharp but not flat. Thickness of the upper unit varies widely across the pit (described by H.C. Hobbs in 2006).

The Cromwell Formation makes up the bulk of the Wisconsinan Superior lobe deposits. It is typically coarse-textured but its texture changes regularly over its extent (Fig. 2), from loam in the Superior basin to sandy loam toward the margin. Once the ice overtopped the rim of the basin, its meltwater consistently flowed away from the ice sheet, with only minor local ponding. Some of the finer material was thus removed from the system in the meltwater, but the ice overrode and reincorporated some of its coarse sediment in the outwash.

The Barnum Formation (which includes the Moose Lake member) is finer-grained than the Cromwell Formation, because the till sheets were deposited by ice that had shrunk back into the Superior basin between advances, and incorporated glacial lake sediment. The Moose Lake member makes up the bulk of the Nickerson and Thomson moraines. In most of these moraines the till is a clay loam diamicton as we see here, but the northeastern part of the Thomson moraine is mainly sand with minor diamicton. Although this site appears to be in a moraine, it is actually an extra-morainic apron. The local relief is due almost entirely to erosion in big diversion channels.

MileageDirections
147.3Continue north on County Road 140.
147.8 At the end of the road, turn left (west) onto CountyRoad 61.
148.5Take the first right onto Old Highway 61.
149.1 Take the first right onto Point Road/TownshipRoad 43.
148.8 At the end of the road, take a right (north) onto County Highway 157.
148.9Turn right into the gravel pit (private property).
MileageDirections
147.3Continue north on County Road 140.
147.8 At the end of the road, turn left (west) onto CountyRoad 61.
148.5Take the first right onto Old Highway 61.
149.1 Take the first right onto Point Road/TownshipRoad 43.
148.8 At the end of the road, take a right (north) onto County Highway 157.
148.9Turn right into the gravel pit (private property).

Stop 4-2. Channel Gravels and Mahtowa Till, Kielty Gravel Pit (15T, 522410 E, 5151500 N)

This pit is dug in the floor of the biggest diversion channel, which has been eroded by a smaller channel (Knaeble and Hobbs, 2009). The pit is wide and fairly shallow over most of its extent, as are most of the pits in these channels. The described face is at the north end, and is deeper than most.

The lowest unit is a clean, medium- to coarse-grained, cross-bedded sand, and contains only a little gravel. Only 90 cm of this sand is exposed. A sharp contact separates a 1.5 m thick, reddish brown (5YR 4/4), non-calcareous, silty, stone-poor diamicton. The upperpart has a thin horizontal platy structure.Texture is (3) 61-33-5 which is quite sandy, but most of the sand is fine, and it looks like the silty Mahtowa member of the Barnum Formation.

A second, sharp contact separates the diamicton from 0.9 to 1.2 m of gravelly sand. The lower part is a cobble-pebble-boulder gravel with a matrix of fine to coarse sand. The upper part is better-sorted clast-supported gravel with a sand matrix. Bedding is obscure or absent. Clasts are primarily red and black and sourced from Lake Superior basin bedrock. Some of the clasts are badly weathered and crumbly, mostly gabbro.

Above this gravelly sand is a gravelly silt unit, 30–45 cm thick. It was probably deposited as loess after the area was exposed, and the small stones were worked up from the gravel below by soil turbation processes (described by H.C. Hobbs in 2006).

Assuming that the diamicton at this site actually represents the Mahtowa member, this channel must have been in existence before the most recent flood excavation. The eroded top of the Mahtowa member is ∼1115 ft (340 m) in the pit, but where it forms the surface till nearby its elevation ranges from 1200 ft (366 m) to over 1250 ft (381 m). Eroding 30 m of the member is not a reasonable interpretation, because it generally is thinner than 6 m. Sand underneath the till was presumably deposited in this earlier channel. Presumably this earlier channel drained a glacial lake in the Superior basin during one of the recessional phases between ice advances.

The poorly sorted gravel is the bedload of the more recent downcutting event. Its bedding and sorting are typical of catastrophic flood deposits described by Lord and Kehew (1987). The source of the flood could be from major downcutting of the outlet to glacial Lake Aitkin-Upham, or from spillage from glacial Lake Koochiching (the eastern arm of Agassiz).

MileageDirections
148.9Continue to head north on County Highway 157 to Little Road/Township Road.
149.1Take the first left (west) onto Little Road/Township Road.
149.4Turn left into the private drive to enter the sand pit (private property).
MileageDirections
148.9Continue to head north on County Highway 157 to Little Road/Township Road.
149.1Take the first left (west) onto Little Road/Township Road.
149.4Turn left into the private drive to enter the sand pit (private property).

Stop 4-3. Channel Sands Covered by Mahtowa and Moose Lake Till (15T, 521600 E, 5151640 N)

This sandpit near the last stop is dug into the edge of the diversion channel. The lowest exposed unit (2.7 m) is a very clean reddish brown (5YR 5/4), non-calcareous, fine sand. It exhibits climbing ripples and flat bedding. The upper part of the unit is very fine sand and silt. The sand here is lighter colored with reddish streaks (lamellae?). Similar to Stop 4-2, this unit sand is overlain by a thin (0.3 m) layer of diamicton ascribed to the Mahtowa member. It is reddish brown (2.5YR 4/4), non-calcareous, pebbly loam, with horizontal platy structure. The texture is (6) 40-39-21.

The next unit above is a layer of sand and gravel 1.5 m thick. The lower part is coarse sand with a little fine gravel. The upper part is mostly fine to medium gravel. Gravel is vaguely flat-bedded. This unit is overlain by a layer of Moose Lake till ∼1.2 m thick. The diamicton is reddish brown (2.5YR 4/4), non-calcareous slightly pebbly, silty clay loam. Measured textures are (1) 19-48-33 and (2) 18-47-36. Clast lithology is Superior provenance, with light-dark-red ratios of 29-51-19 and 22-38-40 (described by H.C. Hobbs in 2007).

The lower units, fine sand, and Mahtowa diamicton, are similar to the lowest units at Stop 4-2, which indicates this site was actually part of the earlier channel. The overlying sand and gravel may have been deposited in a post-Split Rock, pre-Nickerson channel. These older stratified deposits appear to be ordinary glaciofluvial deposits, indicating that the major floods did not come until later. East of the sketched cut, closer to the channel, the upper till is overlain by thin sandy gravel with a wavy erosional contact. This would be the equivalent of the channel gravel at the last stop, and indicates that the first rush of catastrophic flooding down the channel was too large for the channel to handle at first.

MileageDirections
149.4Take a right on Little Road/Township Road to head back toward Barnum.
149.7Turn right (south) onto County Highway 157.
150.7Turn left (east) onto County Highway 6.
151.6Cross MN-61 and enter Barnum City Park for lunch (Stop 4-4).
151.6Continue east onto County Highway 6.
152.4Merge onto I-35 southbound toward Minneapolis/St. Paul.
225.0Take exit #147 “North Branch/Cambridge” and take a left (east) onto MN-95.
245.5At the intersection with U.S.-8 in Taylor’s Falls, continue straight into the “Glacial Gardens Visitor Center.”
MileageDirections
149.4Take a right on Little Road/Township Road to head back toward Barnum.
149.7Turn right (south) onto County Highway 157.
150.7Turn left (east) onto County Highway 6.
151.6Cross MN-61 and enter Barnum City Park for lunch (Stop 4-4).
151.6Continue east onto County Highway 6.
152.4Merge onto I-35 southbound toward Minneapolis/St. Paul.
225.0Take exit #147 “North Branch/Cambridge” and take a left (east) onto MN-95.
245.5At the intersection with U.S.-8 in Taylor’s Falls, continue straight into the “Glacial Gardens Visitor Center.”

Stop 4-5. Glacial Potholes along the St. Croix River, Interstate State Park, Minnesota (15T, 527270 E, 5027370 N)

We have seen evidence of colossal flows of meltwater on this trip. Where did all that water go? All of these channels eventually flowed into the St. Croix River, en route to the Mississippi River. The glacial St. Croix River channel is typically a mile wide where it cuts through Paleozoic carbonate and sandstone in its lower reaches, and many miles wide where it cuts through glacial sediments farther north (Carney, 1996). In the area of Taylor’s Falls, Minnesota and St. Croix Falls, Wisconsin, it cuts through Precambrian basalt and the channel narrows. At its narrowest, the channel is only a half-mile wide. The flow through this narrow gap must have been incredibly swift, for it excavated giant potholes in solid basalt.

Interstate State Park was established both in Minnesota and Wisconsin to preserve these potholes, which are said to be the largest in the world. There are displays in the visitor center to explain the process of formation, and that will not be repeated here. We will take a short walk from the visitor center parking lot to view the potholes.

MileageDirections
245.5Exit the visitor center and turn left (west) ontoU.S.-8.
267.2Merge onto I-35 southbound.
272.4Take I-35W toward Minneapolis.
296.5Enter downtown Minneapolis.
Endof trip.
MileageDirections
245.5Exit the visitor center and turn left (west) ontoU.S.-8.
267.2Merge onto I-35 southbound.
272.4Take I-35W toward Minneapolis.
296.5Enter downtown Minneapolis.
Endof trip.

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ACKNOWLEDGMENTS

Charles Matsch and Howard Mooers, Department of Geology, University of Minnesota, Duluth, provided helpful reviews that improved the readability of an earlier draft of this manuscript. Many of the stops are on private property, and we are very grateful to the owners for providing us access. The Minnesota Geological Survey provided support for the field work upon which this guidebook is based.

Figures & Tables

Figure 1.

Generalized pattern of late Wisconsin glaciations, with emphasis on the Superior lobe readvances. The figure is adapted from Wright (1972) and Patterson and Johnson (2004).

Figure 1.

Generalized pattern of late Wisconsin glaciations, with emphasis on the Superior lobe readvances. The figure is adapted from Wright (1972) and Patterson and Johnson (2004).

Figure 2.

Till textures of the Cromwell and Barnum Formations and idealized stratigraphy. Data compiled from data on file at the Minnesota Geological Survey.

Figure 2.

Till textures of the Cromwell and Barnum Formations and idealized stratigraphy. Data compiled from data on file at the Minnesota Geological Survey.

Figure 3.

Summary of Lake Superior basin ice margins and chronology (ages in 14C ka B.P.). Dates on the moraines in Ontario are from Lowell et al. (2009). The Grand Marais margin is dated by the Gribben Forest Bed (Lowell et al., 1999). The 10.0 14C ka B.P. dates from the „red clay till“ in Wisconsin and Michigan are from Hack (1965) and Black (1976).

Figure 3.

Summary of Lake Superior basin ice margins and chronology (ages in 14C ka B.P.). Dates on the moraines in Ontario are from Lowell et al. (2009). The Grand Marais margin is dated by the Gribben Forest Bed (Lowell et al., 1999). The 10.0 14C ka B.P. dates from the „red clay till“ in Wisconsin and Michigan are from Hack (1965) and Black (1976).

Figure 4.

Glacial Lake Duluth paleogeography, isobases, and elevation data determined from 10-m Digital Elevation Models from the National Elevation Data set (Gesch, 2007). asl—above sea level.

Figure 4.

Glacial Lake Duluth paleogeography, isobases, and elevation data determined from 10-m Digital Elevation Models from the National Elevation Data set (Gesch, 2007). asl—above sea level.

Figure 5.

Overview of stops for Days 2 and 4. Areas of presumably thicker drift with hummocky topography are shaded white. The other mapped glacial landforms are: lineated bedforms (white), eskers (gray), single ridge end moraines (dashed black and gray) and meltwater and glacial-lake overflow channels (black).

Figure 5.

Overview of stops for Days 2 and 4. Areas of presumably thicker drift with hummocky topography are shaded white. The other mapped glacial landforms are: lineated bedforms (white), eskers (gray), single ridge end moraines (dashed black and gray) and meltwater and glacial-lake overflow channels (black).

Figure 6.

Summary of the Duluth level along Skyline Parkway in Duluth, Minnesota. (A) is modified from Clayton (1984). (B) is a Google Earth screen capture of the Oneota Cemetery in Duluth. (C) is original data of the Lake Duluth terrace extracted from 10-m National Elevation Dataset digital elevation models.

Figure 6.

Summary of the Duluth level along Skyline Parkway in Duluth, Minnesota. (A) is modified from Clayton (1984). (B) is a Google Earth screen capture of the Oneota Cemetery in Duluth. (C) is original data of the Lake Duluth terrace extracted from 10-m National Elevation Dataset digital elevation models.

Figure 7.

Stratigraphic data from LS00-3P section 3, including: X-ray radiograph, varve thickness data, percent calcite from carbon coulometry, and scanning X-ray fluorescence V/Cu and V/Ti ratios. The original core description and varve thickness data is from Breckenridge (2007). The red, massive layer is laminated in the X-ray radiographs. V/Cu ratios were proposed by Breckenridge (2005) to be a proxy for Lake Agassiz influx into Lake Superior (higher V = more Agassiz water and sediment).

Figure 7.

Stratigraphic data from LS00-3P section 3, including: X-ray radiograph, varve thickness data, percent calcite from carbon coulometry, and scanning X-ray fluorescence V/Cu and V/Ti ratios. The original core description and varve thickness data is from Breckenridge (2007). The red, massive layer is laminated in the X-ray radiographs. V/Cu ratios were proposed by Breckenridge (2005) to be a proxy for Lake Agassiz influx into Lake Superior (higher V = more Agassiz water and sediment).

MileageDirections
0Merge onto I-35W northbound near the interchange with I-94 in Minneapolis.
25Continue north on I-35 (which merges with I-35E). This is mile marker #127 of I-35W.
133.2Take the Carlton exit #235, then turn left (west) onto MN-210 to the Black Bear Resort and Casino and turn right (north) to enter the Black Bear Resort and Casino.
MileageDirections
0Merge onto I-35W northbound near the interchange with I-94 in Minneapolis.
25Continue north on I-35 (which merges with I-35E). This is mile marker #127 of I-35W.
133.2Take the Carlton exit #235, then turn left (west) onto MN-210 to the Black Bear Resort and Casino and turn right (north) to enter the Black Bear Resort and Casino.
MileageDirections
00.7Turn left heading east onto MN-210 toward Carlton, Minnesota.Turn right (south) onto 3rd Street/County Road 1.
3.1Turn right into the driveway for the Schaefler and sons gravel pit (private property).
MileageDirections
00.7Turn left heading east onto MN-210 toward Carlton, Minnesota.Turn right (south) onto 3rd Street/County Road 1.
3.1Turn right into the driveway for the Schaefler and sons gravel pit (private property).
Mileage3.1DirectionsTake a right turn (south) onto County Road 1.
6.4Turn right (west) onto County Road 4/Military Road. (The Duluth strandline is ascended on this stretch.)
10.5Turn left (south) onto County Road 103. (The Duluth strandline is descended on this stretch.)
13.6Turn right (west) onto Baker Road (after going down and up the Blackhoof River valley). (The Duluth strandline is readily visible on the right side of the road as we pass the Baker farm.)
14.7Turn left on County Road 104, which turns intoCounty Road 105 after a mandatory right turn.
15.9Turn left (south) onto Pioneer Road.
17Pull over onto the roadside to inspect a borrow pit in the Duluth level wave-cut terrace (private property).
Mileage3.1DirectionsTake a right turn (south) onto County Road 1.
6.4Turn right (west) onto County Road 4/Military Road. (The Duluth strandline is ascended on this stretch.)
10.5Turn left (south) onto County Road 103. (The Duluth strandline is descended on this stretch.)
13.6Turn right (west) onto Baker Road (after going down and up the Blackhoof River valley). (The Duluth strandline is readily visible on the right side of the road as we pass the Baker farm.)
14.7Turn left on County Road 104, which turns intoCounty Road 105 after a mandatory right turn.
15.9Turn left (south) onto Pioneer Road.
17Pull over onto the roadside to inspect a borrow pit in the Duluth level wave-cut terrace (private property).
MileageDirections
17Continue south on Pioneer Road.
17.9At the end of Pioneer Road, take a left turn (east) onto Spring Lake Road/County Road 6. Spring Lake Road doglegs left after 2.4 mi, then right after 1.8 mi.
22.1Do not veer to the left, but continue straight to stay on the gravel Spring Lake Road.
24.1Turn right (south) onto County Road 1.
24.3Turn right on MN-23.
24.8Park on the shoulder above the Deer Creek culvert to inspect the exposed clay bank on the east side of the road in the creek valley.
MileageDirections
17Continue south on Pioneer Road.
17.9At the end of Pioneer Road, take a left turn (east) onto Spring Lake Road/County Road 6. Spring Lake Road doglegs left after 2.4 mi, then right after 1.8 mi.
22.1Do not veer to the left, but continue straight to stay on the gravel Spring Lake Road.
24.1Turn right (south) onto County Road 1.
24.3Turn right on MN-23.
24.8Park on the shoulder above the Deer Creek culvert to inspect the exposed clay bank on the east side of the road in the creek valley.
MileageDirections
24.8Turn around to backtrack north on MN-23.
31.0Turn right (east) onto County Road 4/MilitaryRoad.
32.9Turn left (north) onto the BNSF access road (permission is necessary to access).
33.7Park in a clearing and walk 0.2 mi to a gully on the east side of the railway.
MileageDirections
24.8Turn around to backtrack north on MN-23.
31.0Turn right (east) onto County Road 4/MilitaryRoad.
32.9Turn left (north) onto the BNSF access road (permission is necessary to access).
33.7Park in a clearing and walk 0.2 mi to a gully on the east side of the railway.
MileageDirections
33.7Turn around and head south back to County Road 4/Military Road.
34.8Turn right (west) onto County Road 4/Military Road.
36.8Turn right (north) onto MN-23. Continue to West Duluth.
52.0Turn left (north) onto N 59th Avenue W in the city of West Duluth.
52.8Turn left (west) onto Highland Street.
53.1Take the first right (north) onto N 64th Avenue W into the Oneota Cemetary.
MileageDirections
33.7Turn around and head south back to County Road 4/Military Road.
34.8Turn right (west) onto County Road 4/Military Road.
36.8Turn right (north) onto MN-23. Continue to West Duluth.
52.0Turn left (north) onto N 59th Avenue W in the city of West Duluth.
52.8Turn left (west) onto Highland Street.
53.1Take the first right (north) onto N 64th Avenue W into the Oneota Cemetary.
MileageDirections
53.1Exit the cemetery by turning left (east) onto Highland Street.
53.9Turn right (south) onto N 59th Avenue W.
54.7Turn right (west) onto Grand Avenue/MN-23.
54.9Take a sharp left to merge onto I-35 northbound.
58.6Take Exit #256B for 5th Ave. W toward Lake Ave.
59.1Turn right onto Harbor Drive, then left at the stoplight onto W Commerce.
59.2Turn right (south) onto Lake Avenue S and continue over the Lift Bridge, and onto Minnesota Avenue.
63.4Park in the Park Point parking lot.
MileageDirections
53.1Exit the cemetery by turning left (east) onto Highland Street.
53.9Turn right (south) onto N 59th Avenue W.
54.7Turn right (west) onto Grand Avenue/MN-23.
54.9Take a sharp left to merge onto I-35 northbound.
58.6Take Exit #256B for 5th Ave. W toward Lake Ave.
59.1Turn right onto Harbor Drive, then left at the stoplight onto W Commerce.
59.2Turn right (south) onto Lake Avenue S and continue over the Lift Bridge, and onto Minnesota Avenue.
63.4Park in the Park Point parking lot.
MileageDirections
59.2Head back north on Minnesota Avenue toward Duluth.
62.5Do not veer right onto Lake Avenue, but continue north on Minnesota Avenue.
62.8Park outside the gates to the U.S. Army Corps of Engineers dock.
MileageDirections
59.2Head back north on Minnesota Avenue toward Duluth.
62.5Do not veer right onto Lake Avenue, but continue north on Minnesota Avenue.
62.8Park outside the gates to the U.S. Army Corps of Engineers dock.
MileageDirections
62.8Head northwest onto Minnesota Avenue. Take the first right, then the next left to get back onto S. Lake Avenue.
63.3Cross the Aerial Lift Bridge, and continue to head north on Lake Avenue.
63.8Turn right on W Commerce Street/W Lake Place.
63.9Turn left (north) onto N Lake Avenue, then take a right to merge onto I-35 northbound.
66.4Continue onto MN-61/London Road, and continue onto the MN-61 Expressway.
79.6Turn left (north) onto Homestead Road.
84.3Turn left (west) onto Clover Valley Road.
85.2Continue to the end of Clover Valley Road and enter the Peterson gravel pit (private property).
MileageDirections
62.8Head northwest onto Minnesota Avenue. Take the first right, then the next left to get back onto S. Lake Avenue.
63.3Cross the Aerial Lift Bridge, and continue to head north on Lake Avenue.
63.8Turn right on W Commerce Street/W Lake Place.
63.9Turn left (north) onto N Lake Avenue, then take a right to merge onto I-35 northbound.
66.4Continue onto MN-61/London Road, and continue onto the MN-61 Expressway.
79.6Turn left (north) onto Homestead Road.
84.3Turn left (west) onto Clover Valley Road.
85.2Continue to the end of Clover Valley Road and enter the Peterson gravel pit (private property).
MileageDirections
85.2Turn around and head back to MN-61 via Clover and Homestead roads.
90.0Turn left (northeast) onto MN-61.
93.6Turn left (north) onto Hawkhill Road.
MileageDirections
85.2Turn around and head back to MN-61 via Clover and Homestead roads.
90.0Turn left (northeast) onto MN-61.
93.6Turn left (north) onto Hawkhill Road.
MileageDirections
94.7Turn around and head back to MN-61 via Hawkhill Road.
95.8Turn left (northeast) onto MN-61.
103.3Enter Two Harbors for dinner, then head northeast on MN-61 toward Grand Marais, Minnesota.
185.3Arrive at Hotel in Grand Marais.
Endof Day 2.
MileageDirections
94.7Turn around and head back to MN-61 via Hawkhill Road.
95.8Turn left (northeast) onto MN-61.
103.3Enter Two Harbors for dinner, then head northeast on MN-61 toward Grand Marais, Minnesota.
185.3Arrive at Hotel in Grand Marais.
Endof Day 2.
MileageDirections
0Turn left and head south on MN-61.
106Turn left to merge onto I-35 southbound.
146Take Exit #220 (Barnum), and turn right (west) at the exit onto County Road 6/Main Street.
146.1Take the first right (north) on to County Road 140.
147.3Turn right into the borrow pit after Buck Road (private property).
MileageDirections
0Turn left and head south on MN-61.
106Turn left to merge onto I-35 southbound.
146Take Exit #220 (Barnum), and turn right (west) at the exit onto County Road 6/Main Street.
146.1Take the first right (north) on to County Road 140.
147.3Turn right into the borrow pit after Buck Road (private property).
MileageDirections
147.3Continue north on County Road 140.
147.8 At the end of the road, turn left (west) onto CountyRoad 61.
148.5Take the first right onto Old Highway 61.
149.1 Take the first right onto Point Road/TownshipRoad 43.
148.8 At the end of the road, take a right (north) onto County Highway 157.
148.9Turn right into the gravel pit (private property).
MileageDirections
147.3Continue north on County Road 140.
147.8 At the end of the road, turn left (west) onto CountyRoad 61.
148.5Take the first right onto Old Highway 61.
149.1 Take the first right onto Point Road/TownshipRoad 43.
148.8 At the end of the road, take a right (north) onto County Highway 157.
148.9Turn right into the gravel pit (private property).
MileageDirections
148.9Continue to head north on County Highway 157 to Little Road/Township Road.
149.1Take the first left (west) onto Little Road/Township Road.
149.4Turn left into the private drive to enter the sand pit (private property).
MileageDirections
148.9Continue to head north on County Highway 157 to Little Road/Township Road.
149.1Take the first left (west) onto Little Road/Township Road.
149.4Turn left into the private drive to enter the sand pit (private property).
MileageDirections
149.4Take a right on Little Road/Township Road to head back toward Barnum.
149.7Turn right (south) onto County Highway 157.
150.7Turn left (east) onto County Highway 6.
151.6Cross MN-61 and enter Barnum City Park for lunch (Stop 4-4).
151.6Continue east onto County Highway 6.
152.4Merge onto I-35 southbound toward Minneapolis/St. Paul.
225.0Take exit #147 “North Branch/Cambridge” and take a left (east) onto MN-95.
245.5At the intersection with U.S.-8 in Taylor’s Falls, continue straight into the “Glacial Gardens Visitor Center.”
MileageDirections
149.4Take a right on Little Road/Township Road to head back toward Barnum.
149.7Turn right (south) onto County Highway 157.
150.7Turn left (east) onto County Highway 6.
151.6Cross MN-61 and enter Barnum City Park for lunch (Stop 4-4).
151.6Continue east onto County Highway 6.
152.4Merge onto I-35 southbound toward Minneapolis/St. Paul.
225.0Take exit #147 “North Branch/Cambridge” and take a left (east) onto MN-95.
245.5At the intersection with U.S.-8 in Taylor’s Falls, continue straight into the “Glacial Gardens Visitor Center.”
MileageDirections
245.5Exit the visitor center and turn left (west) ontoU.S.-8.
267.2Merge onto I-35 southbound.
272.4Take I-35W toward Minneapolis.
296.5Enter downtown Minneapolis.
Endof trip.
MileageDirections
245.5Exit the visitor center and turn left (west) ontoU.S.-8.
267.2Merge onto I-35 southbound.
272.4Take I-35W toward Minneapolis.
296.5Enter downtown Minneapolis.
Endof trip.

Contents

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