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Report 381, Plate BAitkin County Aggregate Resources,

Crushed-Stone Potential

Minnesota Department of Natural ResourcesDivision of Lands and MineralsDirector, Jess Richards

Copyright 2015 State of Minnesota, Department of Natural ResourcesProducts of this project include a CD/ROM with digital maps, GIS data, and metadata

Plate A, Report 381, Aitkin County Aggregate Resources, Sand and Gravel Potential and Plate B, Report 381, Aitkin County Aggregate Resources, Crushed-Stone Potential

0 1 2 3 4 5 6Miles

0 1 2 3 4 5 6 7 8 9Kilometers

Printed Map Scale 1:100,000Based on a 1:100,000 scale resource assessment

PLATE B: AITKIN COUNTY AGGREGATE RESOURCES,

CRUSHED-STONE POTENTIAL

St. Paul, Minnesota - June 2015Carrie E. Jennings and Steven J. Kostka

Produced by the Aggregate Resource Mapping Program,Division of Lands and Minerals, Minnesota

Department of Natural Resources

SUMMARYWhere suitable bedrock crops out or is within 50 feet of the surface as indicated from logs of borings or well records, it has the potential to serve as a crushed-stone resource. The general suitability of the bedrock involves its lithology and durability. Geologic maps and associated reports from the Minnesota Geological Survey (MGS) are a reliable source of bedrock information and were the primary source of information used (Southwick and others, 1988; Boerboom and others, 1999). Various metamorphic, plutonic and volcanic bedrock types of the Little Falls Formation (Paleoproterozoic), Mille Lacs Group (Paleoproterozoic), and McGrath Gneiss (Neoarchean) are near the surface in the southern third of Aitkin County. Bedrock is deeply buried in the rest of the county.

PURPOSEThe purpose of this project is to map crushed-stone bedrock potential and is part of a larger project to identify construction aggregate resources in Aitkin County, Minnesota. The Minnesota Department of Natural Resources (DNR), directed by Minnesota Statutes, section 84.94 “Aggregate Planning and Protection,” provides counties with needed informa-tion to plan for the future availability of aggregate resources. Crushed-stone is produced by mechanically crushing durable bedrock into desired-sized, angular particles that can meet the specifications for construction aggregate used in building roads, bridges, airport runways and railroad beds, for example. Crushed-stone resources are not evenly distributed across the state of Minnesota or within a single county. Therefore, determining the location of the bedrock with crushed-stone potential within a county is for planning and land-use decisions.

This plate displays the distribution of crushed-stone bedrock potential within 50 feet of the land surface. The crushed-stone potential of any location within the county depends on the physical and compositional characteristics of the bedrock along with how deeply the bedrock is buried. For example, some of the gneissic rocks exposed in Aitkin County provide durable, high-quality, crushed-stone that meets Minnesota Department of Transportation (MnDOT) specifications for a Class A aggregate source. Other rock types, like metamorphosed sedimentary rocks, can be soft, flaky, and not durable enough to be used for aggregate. Also, the crushed-stone potential decreases the more deeply the rock is buried by sediment, sedimentary rock, and/or highly weathered bedrock.

This reconnaissance-level assessment shows the distribution of crushed-stone potential within Aitkin County. Geologic data, such as exposed bedrock locations, subsurface water well data, available drill core samples, geophysics, previous geologic studies, and verbal com-munication with other geologists, and local aggregate producers, provided the basis for the criteria that were used to define crushed-stone potential. Mapped crushed-stone potential defines an area where the geologic evidence was interpreted to support a particular map designation. This map is not intended to provide the kind of site-specific information that would be required to determine the value or suitability of a potential crushed-stone quarry at individual sites. The mineralogy of the rock was not explicitly considered, that is, which minerals may be present and susceptible to weathering or freeze-thaw failure after crushing. Other site-specific factors can include land ownership, the owner’s preferences, biodiversity significance, royalty rates, distance to market, permitting requirements, and/or the cultural and historical significance of the location. Factors such as the economic feasibility of mining a given crushed-stone resource may depend on transportation distances to a potential end user as well as the proximity of a permitted mining operation to existing transportation modes or corridors.

GEOLOGIC OVERVIEWAitkin County bedrock is located within the Paleoproterozoic Penokean Orogen (see figure 1), a belt of deformed and metamorphosed bedrock related to crustal collision dating to 2,100 Ma (million years from present) to 1,800 Ma. In southcentral Aitkin County there are bedrock exposures of McGrath Gneiss which was formed from an older event dating to between 2,700 Ma to 2,500 Ma within the Neoarchean period. These two areas are inter-rupted by rocks associated with the later, Mesoproterozoic Keewenawan Supergroup of the Midcontinent Rift System, which originated as a continent-splitting rift filled with lava flows and overlying sand (1,100 Ma) (Boerboom, 2009). The bedrock geology is comprised of four major terranes that represent these three early events:

1) Superior Province - Neoarchean McGrath Gneiss bedrock is a granitic to granodiorite orthogneiss from the Superior Province period formed between 2,700 Ma to 2,500 Ma.

2) Paleoproterozoic sedimentary bedrock dominated by graywacke-slate of the Thomson Formation that comprise the southern portion of the Animikie Basin and unconformably overlie the metamorphosed sedimentary and igneous rocks of the Paleoproterozoic Mille Lacs Group;

3) The Mille Lacs Group, a complex of deformed fold and thrust belts involving sedimentary and volcanic bedrock of Paleoproterozoic age associ-ated with collision and subduction that are separated by major structural discontinuities that include increasingly metamorphosed and plutonic terranes to the SE: North Range, Cuyuna District; South Range Cuyuna District, Moose Lake-Glen Township Structural panel; and McGrath-Little Falls struc-tural panel (Southwick and others, 1988);

4) Mesoproterozoic Keewenawan sandstone, a rift-filling, quartzose sand-stone, siltstone and conglomerate that is jointed and reversely faulted in places.

METHODSSince aggregate resources are mined from the earth, geologic methods are required to deter-mine the location, distribution, and quality of a potential aggregate source. At this reconnais-sance level (1:100,000) assessment, three geologic criteria were used to determine crushed-stone potential: bedrock type from existing bedrock mapping, depth of burial, and probabil-ity of occurrence based on the availability of data. Different bedrock types have different physical properties (e.g. hardness, durability, and chemical composition). To be suitable for use as a construction aggregate, a rock must be hard, durable, not fracture in a predominant direction or react chemically.

The quantity, quality, and distribution of the data available to us determined the confidence level or probability of the crushed-stone potential designation. General trends in the suitabil-ity, or quality, of bedrock as a source for crushed-stone resources were interpreted from exist-ing geologic information and MnDOT specifications.

An existing depth to bedrock model (Jirsa and others, 2010) predicted where crystalline bedrock was within 50 feet of the land surface. Much of the subsurface information used for the model came from the County Well Index (CWI), an online database developed and maintained by the Minnesota Department of Health (MDH) and MGS. CWI contains basic geologic and stratigraphic information for over 300,000 domestic and municipal water wells drilled throughout Minnesota. The CWI identifies wells as being either located or unlocated. Located CWI wells are field-verified under the supervision of the MGS. Unlocated CWI wells have not been field-verified, but their records may contain information that can be used to associate a well with a given address or parcel of land. For this project, unlocated wells were integrated into the existing depth-to-bedrock model (Jirsa and others, 2010) if the location of a well record could be reasonably verified using parcel data from county tax records, address information, plat maps, air photographs, and road maps. When correlation was established, the well was placed near a residential dwelling within the parcel. This method of locating wells is not as accurate as field checking using 7.5 Minute USGS Quad-rangle maps and/or Global Positioning System (GPS). However, the level of accuracy is within an acceptable range for this reconnaissance-level assessment.

Of the bedrock units mapped within the county, only 5 bedrock types were shallowly buried or exposed; McGrath Gneiss, Little Falls Formation, Glen Township Metabasalt, Dam Lake Quartzite, and Paleoproterzoic Iron-formation. They can be classified using MnDOT’s system wherein Class A crushed-stone ranks as the highest quality aggregate (MnDOT 3139.2 A2a) and is defined as crushed-stone derived from listed rock types like basalt, diabase, gabbro, quartzite and granite. Class A aggregates are highly valued because they meet rigorous specifications for high performance pavement mix designs required for Superpave and other applications. All other rock types, (e.g. schist, carbonate, and rhyolite) are classified as Class B aggregates. However, for a bedrock source at any given location to be qualified as a certified aggregate source for concrete, the material must undergo testing and meet MnDOT specifications (MnDOT Standard Specifications for Construction, 2005). This type of testing was not performed as part of this project. Therefore, the final determination of crushed-stone quality was assessed on a relative scale from “low” to “high” within the crushed-stone potential classification system.

BASE MAP DATA SOURCES Lakes, rivers, streams, and drainage ditches from NWI (National Wetland Inventory), MnDOT Base map, DNR 24K Streams, compiled at 1:24,000 from aerial photography (1979-1988) and USGS quadrangle maps (1980-1990); PLS (Public Land Survey) townships and sections layers extracted from PLS Project, 2001, DNR, Division of Lands and Minerals; Cities were derived from the GNIS (Geographic Name Information System) by pulling out the features that were coded as populated places. A selected subset of these was used for this map, 2003; County boundaries from DNR, derived from combination of 1:24,000 scale PLS lines, 1:100,000 scale TIGER, 1:100,000 scale DLG, and 1:24,000 hydrography lines, 1993; Hydrography labels derived from selected MnDOT County Highway Maps water feature annotations, 2002; Roads from MnDOT Base map, Fall of 2006; Railroad Tracks from MnDOT Base map, 2001. GIS support and cartography by Kevin J. Hanson, DNR, Division of Lands and Minerals.

MAP AND DATA DISCLAIMERThe State of Minnesota makes no representations or warranties express or implied, with respect to the use of the information contained herein regardless of its format or the means of its transmission. There is no guarantee or representation to the user as to the accuracy, currency, suitability, completeness, usefulness, or reliability of this information for any purpose. The user accepts the information “as is." The State of Minnesota assumes no responsibility for loss or damage incurred as a result of any user’s reliance on this information. All maps, reports, data, and other information contained herein are protected by copyright. Permission is granted to copy and use the materials herein for any lawful noncommercial purpose. Any user of this information agrees not to transmit or provide access to all or any part of this information to another party unless the user shall include with the information a copy of this disclaimer.

METHODS, CONTINUEDThe MGS depth to bedrock model (Jirsa and others, 2010) calculates the bedrock-surface elevation and then subtracts it from the ground-surface elevation to produce an approximation of overburden thickness. Crushed-stone potential was delineated where crystalline bedrock was interpreted to be within 0 to 15 feet, 16 to 30 feet, and 31-50 feet. Bedrock that was buried by more than 50 feet was not considered. These intervals were intended to reflect current trends in mining and general water-table elevations.

The accuracy of both the overburden-thickness model and the crushed-stone poten-tial derived from this model rely upon the distribution and density of data points. The more data within an area, the greater the probability that crushed-stone resources exist at the depth described within the map unit. There remains some uncertainty owing to the variability of bedrock topography. In some areas, the bedrock surface is irregular and may have significant relief and be partially buried by glacial sediment. Every effort was made to accurately capture trends in sediment thickness. The probability is a relative assessment that ranges from low to high, based on the quantity, quality, and distribution of information associated with a map unit. The assessment of crushed-stone potential integrates the three criteria of bedrock type, sediment thickness, and probability into a classification system where areas within Aitkin County were classified as having high, moderate, low or limited crushed-stone potential. Areas designated as high or moderate potential were consid-ered to be significant crushed-stone resources, while areas classified as low or limited potential were considered to be nonsignificant crushed-stone resources.

Bedrock Outcrop Areas in Aitkin County

Outcrops of the McGrath Gneiss: Located near the towns of McGrath, Pliny, and SolanaIn the south central portion of the county, Neoarchean McGrath gneiss bedrock, a granitic to granodioritic orthogneiss is at or near the surface on the up-ice (north-facing) side of a streamlined upland. This is a Class A rock type and has the highest crushed-stone potential in the county. Jointed and weathered exposures of the McGrath gneiss were found near the towns of McGrath, Pliny, and Solana. The McGrath Gneiss bedrock is less than 50 feet from the surface over much of the rest of the broad highland and a broad valley extending southwest from it. The broad upland in Section 6 of Idun Township along the Aitkin-Mille Lacs border and sections 34-36 of Millward Township along the Aitkin-Pine County border are areas of shallowly buried, pink to gray, medium-to-coarse-grained gneiss that is locally sheared, crushed and recrystallized.

Photos of McGrath Gneiss near the town of McGrath

Photos of McGrath Gneiss near the town of Pliny

Photos of McGrath Gneiss near the town of Solana

Outcrops of the Little Falls Formation In the central part of the county there is a small outcrop of Paleoproterozoic Little Falls Formation which includes metamorphosed graywacke and mudstone, schist and slate. The exposures are on the up-ice side of an upland in glacially streamlined terrane. The fine-grained, platy and schistose nature of this Formation makes the quality of them less desirable for crushed-stone; it falls within Class B and is of low potential where it outcrops.

Outcrops of the Glen Township MetabasaltsSouthwest of Rice Lake and along the shores of Long Lake there are shallow bedrock areas where Glen Township metabasalt and associated metasedimentary rocks and Paleoproterozoic Iron-formation in the Penokean fold and thrust belt subcrop. The DNR was unable to view and sample these outcrops due to them being located on private land. According to Terry Boerboom at the MGS, who mapped the bedrock geology here, these bedrock outcrops are all mafic hypabyssal intrusive rocks and their schistose nature makes the quality of them less desirable for crushed-stone resources. Outcrops of the Dam Lake QuartziteWest of Dam Lake are isolated exposures of the Dam Lake Quartzite, a Paleoproter-zoic metasedimentary rock. It is also part of the Penokean fold and thrust belt. MnDOT defines Quartzite as a Class A rock type. One of the outcrops is on the lake shore, the other outcrop is just off the road in the woods. Geologists of the DNR were unable to view and sample these outcrops. Terry Boerboom at the MGS who viewed and mapped the outcrops stated that they are fairly course-grained and pretty well annealed. Based on this correspondence, and MnDOT’s Class A rock type determination, the DNR interprets the Dam Lake Quartzite here as having moderate potential for crushed-stone resources where it is near the surface (0-15 feet).

BEDROCK OUTCROPS, DEPTH TO BEDROCK, AND BEDROCK GEOLOGY

Several Minnesota Geological Survey bedrock geology GIS datasets along with DNR field work were used to interpret the crushed-stone potential of Aiktin County. They include bedrock outcrops, CWI wells that encounter bedrock, a depth-to-bedrock (see figure 2) model, and bedrock geology. The bedrock geology depicted here is a simplified version of a 1:500,000 scale map produced by the MGS (Jirsa and others, 2010). The map does not show structural data such as faults. These datasets are presented on this map for reference.

MGS and/or DNR bedrock outcrops: Due to the scale of the map the bedrock outcrop locations are shown with the label ‘Outcrops’ & a leader line to their general location. Those that were sampled have a leader line with a bolded label ‘Outcrop Samples’.

MGS mapped outcropsDNR mapped outcrops

MGS CWI wells that encounter bedrock (n=67)Labeled by depth to bedrock in feet (see figure 2)

Depth to bedrock contours generalized: 25 foot intervals

BEDROCK GEOLOGY LEGENDMESOPROTEROZOIC AND PALEOPROTEROZOIC ROCKS

Highlighted in Bold are bedrock types that generally have physical characteristics suitable for producing Class A aggregates

MESOPROTEROZOICMss Sandstone, siltstone, and local conglomerate. Includes the Hinckley Sandstone and Fond du Lac FormationsMmi Mafic intrusive stock; diabase, diorite, pyroxenite, gabbro

PALEOPROTEROZOICPmi Mafic intrusion; pyroxenite, peridotite, gabbro, and lamprophyre. Defined largely by magnetic signature

East-central Minnesota batholithPgd Gray granodioritic to dioritic intrusion; Isle and Warman granite

Animikie GroupPas Virginia, and Thomson formations, mudstone and graywackePag Slate, graywacke twice deformed metasedimentary rocksPsi Sulfidic iron-formation, graphitic argillite, slatePgs Graywacke, slate with graphitic and sulfidic zones

Little Falls FormationPls Of graywacke, mudstone, and schist and slate protolithPmd Denham Formation; sandstone, marble, schist

Mille Lacs and North Range Groups in the fold and thrust belt of the Penokean Orogen

Pm Mudstone, quartzite, graywacke, phyllite, graphitic argillitePif Iron-formation, interbedded with mafic volcanic and hypabyssal intrusive rocksPmv Mafic metavolcanic and hypabyssal intrusive rocks, argillite, slate, graywackePmq Dam Lake QuartzitePvs Interlayered metasedimentary and metavolcanic rocksPml Mille Lacs Granite

NEOARCHEAN ROCKS

Agn McGrath Gneiss - Granitic to granodioritic orthogneiss

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N o r t h - h a l f o f A i t k i n C o u n t y n o t s h o w n d u e t o l i m i t e d p o t e n t i a l f o r c r u s h e d - s t o n e r e s o u r c e s

CRUSHED-STONE POTENTIALCrushed-stone potential is based on interpreting existing geologic data, MnDOT Specification for Class A Aggregate (MnDOT 3139.2 A2a), and geologic observa-tions of bedrock outcrops made in the field. This reconnaissance-level assessment does not imply that crushed-stone resources exist everywhere within a given map unit designated as “Potential Crushed-Stone Resources.” Rather, that geologic condi-tions exist at the map scale such that crushed-stone resources are reasonably expected to occur somewhere within the map unit. Since this is a reconnaissance-level survey, site-specific evaluations are still necessary prior to any development of this resource, especially in regards to aggregate quality or environmental review. Factors such as ownership, zoning, protected waters, wetlands, and other individual site characteristics are not part of the geological resource data summarized here.

SIGNIFICANT CRUSHED-STONE POTENTIAL: Includes high and mod-erate potential map units. The following bedrock lithologic types are interpreted to have significant potential for crushed-stone resources: granite, granitic gneiss, quartzite, and mafic to ultramafic intrusive rock. These bedrock types generally have physical characteristics suitable for producing Class A aggregates. In Aitkin County there are granitic rocks (Pgl-Mille Lacs Granite, Pgd- Isle and Warman Granite), granitic gneiss rocks (Agn- McGrath Gneiss), quartzite (Pmq- Dam Lake Quartzite), and mafic intrusive rocks (Pmi). High or moderate crushed-stone poten-tial map units also need to be either exposed at the surface or be covered by less than 30 feet of overburden. Only the McGrath Gniess and Dam Lake Quartzite are exposed at the surface or interpreted to be covered by less than 30 feet of overbur-den in Aitkin County. DNR geologists viewed and sampled McGrath Gneiss in three areas of the county. They were not able to view the Dam Lake Quartzite outcrops displayed on the map but did correspond with Terry Boerboom at the MGS who mapped those outcrops. None of the McGrath Gneiss outcrop samples were tested for construction aggregate quality specifications according to MnDOT and therefore should be considered Class A aggregate candidates.

High Crushed-Stone Potential: Includes McGrath Gneiss exposed at the land surface or buried by less than 15 feet of overburden. The interpreted quality of this bedrock type is moderate. The probability of crushed-stone existing within a map unit ranges from moderate to high.

Moderate Crushed-Stone Potential: Can include either of the follow-ing criteria:• McGrath Gneiss buried beneath 15 to 30 feet of overburden or,• Dam Lake Quartzite exposed at the land surface or,• Dam Lake Quartzite buried by less than 15 feet of overburden.

The interpreted quality of these two bedrock types are moderate. The probability of crushed-stone resource existing within a map unit ranges from moderate to high.

NONSIGNIFICANT CRUSHED-STONE POTENTIAL: Includes low and limited potential map units. Nonsignificant is a term used in this assessment to define mapped areas that contain any of the following conditions: poor quality bedrock units, moderate quality bedrock units with thick overburden (>30 feet), or areas where higher potential may exist but cannot be verified due to a lack of substantiating data which facilitate a lower probability rating. Poor quality bedrock units exposed at the surface, or are buried by less than 15 feet of overburden, include metasedimentary and metavolcanic rocks in the Little Falls Formation.

Low Crushed-Stone Potential: Can include either of the following criteria:• McGrath Gneiss buried by 30 to 50 feet of overburden or,• Little Falls Formation bedrock exposed at the land surface or, • Little Falls Formation buried by less than 15 feet of overburden.

Low potential also includes areas with little supporting data to substantiate a higher potential classification. The interpreted rock quality ranges from poor to moderate. The probability that these rock types occur within the map unit ranges from low to high.

Limited Crushed-Stone Potential: Not symbolized on the map. Includes all other rock types seen in bedrock geology legend with varying thickness of overburden (15 to >50 feet). The interpreted quality ranges from poor to moderate. The probability of crushed-stone existing within a mapping unit ranges from low to moderately low.

ACKNOWLEDGEMENTS Doug Rosnau assisted both geologists in the field by uncomplainingly drilling, driving and digging under all conditions. The continuity provided by him assisting both geologists, who worked separately on this project, was invaluable.

REFERENCES Arends, H.E., 2008. Aggregate Resources, Crushed-Stone Potential, Mille Lacs County, Minnesota. Report 366, Plate A. Minnesota Department of Natural Resources, Division of Lands and Minerals, Scale 1:100,000 with digital data. http://files.dnr.state.mn.us/lands_minerals/mille_lacs_plate_b.pdf

Boerboom, T.J., 2010. Latest bedrock geologic map of Carlton County, East-Central Minnesota and revisions to the south Animikie Basin edge [abstract]: Institute on Lake Superior Geology Proceedings, 50th Annual Meeting, International Falls, Minnesota. v. 56, part 1, p. 1-2.

Boerboom, T.J., 2009. Bedrock Geology, in, T. J. Booerboom, project manager, Geologic Atlas of Carlton County and the southern portion of St. Louis County, Minnesota Geological Survey County Atlas Series, C-19, Part A, 1:

Boerboom, T.J., Southwick, D.L., and Severson, M.J., 1999. Bedrock Geology of the Mille Lacs 30x60 minute quadrangle, east-central Minnesota: Minnesota Geological Survey Miscellaneous Map Series, M-100, 1:100,000.

Hinze, W.J., Allen, D.J., Braile, L.W., and Mariano, J., 1997. The Midcontinent rift system: A major Proterozoic continental rift, in Ojakangas, R.W., Dickas, A.B., and Green, J.C., eds., Middle Proterozoic to Cambrian rifting, central North America: Geological Society of America Special Paper 312, p. 7–35.

Jirsa, M.A., Boerboom, T.J., Chandler, V.W., Mossler, J.H., Runkel, A.C., and Setterholm, D.R., 2011. Geologic Map of Minnesota—Bedrock Geology. Minnesota Geological Survey State Map Series S-21, 1:500,000.

Jirsa, M.A., Bauer, E.J., Boerboom, T.J., Chandler, V.W., Lively, R.S., Mossler, J.H., Runkel, A.C., and Setterholm, D.R., 2010. Preliminary Bedrock Geologic Map of Minnesota—Depth to Bedrock of Minnesota. Minnesota Geological Survey Open-File Report OFR10_02, 1:500,000.

Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1998. Geologic map (scale 1:250,000) of the Penokean Orogen, central and eastern Minnesota, and accompanying text. Minnesota Geological Survey Report of Investigations 37, St. Paul, Minnesota, 32 p.

Figure 1: DNR graphic of MGS relevant bedrock terranes in Aitkin and surrounding counties (adapted from Jirsa and others, 2010).

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Transportation FeaturesInterstate HighwayUS Highway

MN HighwayCounty Highwaysand RoadsTownship and Other RoadsMunicipal RoadsRailroad Tracks

BASE MAP SYMBOLS Symbols may appear in different shades due to the overlaid layers of

bedrock geology and/or crushed stone potential.

County Seat & CitiesCounty Seat Cities

Physical FeaturesLakes Rivers & StreamsTopographic Relief

Bounding FeaturesCounties PLS Townships PLS Sections

(Aitkin)

(Cedar Lake)

(McGrath)

(Stony Creek)

(1,6,31,36)

( Idun)(KANABEC COUNTY)

Map Extent in Orange:Only displaying the southern portion of Aitkin Countydue to limited potential forcrushed-stone resources in thenorthern half of Aitkin County.

Aitkin County, MinnesotaAitkin County, Minnesota

Cass

Pine

St. Louis

Itasca

Carlton

Crow Wing

Morrison Kanabec

Mille Lacs

Aitkin

Dam Lake Quartzite

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OutcropSamples

Outcrops

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OutcropSamples

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McGrath Gneiss Ouctcrops - McGrath Area

Little Falls Formation Outcrops

McGrath Gneiss Ouctcrops - Solana Area

Glen Township MetabasaltOutcrops

Dam Lake Quartzite Outcrops

McGrath Gneiss Ouctcrops - Pliny Area

See map for location labeled “McGrath Gneiss Ouctcrops - McGrath Area” in Township 43, Range 24, Section 1. Samples were taken at this site. The small samples collected provide a visual example of the outcrop observed, but are not intended to be representative for testing purposes.

See map for location labeled “McGrath Gneiss Ouctcrops - Pliny Area” in Township 44, Range 23, Section 6. Samples were taken at this site. The small samples collected provide a visual example of the outcrop observed, but are not intended to be representative for testing purposes.

See map for location labeled “McGrath Gneiss Ouctcrops- Solana Area” in Township 45, Range 22, Section 35. Samples were taken at this site.

Conceptual graphic

BEDROCK

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Figure 2: Depth to Bedrock Conceptual Graphic