Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-48, PART A GEOLOGICAL SURVEY THE NOBLES COUNTY BOARD OF COMMISSIONERS, Harvey Thorleifson, Director THE MINNESOTA DEPARTMENT OF NATURAL RESOURCES, AND Nobles County THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND Plate 6—Bedrock Topography AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES and Depth to Bedrock

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ESTON W. MURRAY 96° W. 95° 52' 30" W. 95° 45' W. 95° 37' 30" W. 95° 30' MURRAY COTTONWOOD

PIP COUNTY COUNTY R. 43 W. R. 42 W. R. 41 W. R. 40 W. R. 39 W. COUNTY COUNTY D D D D D D 440 ROCK Willow Dundee JACKSON Lake COUNTY 500 COUNTY 6 540 1 6 1 6 1 1 6 6 440 520 1 460

520 520 Ju 440 dicia 480 l D BEDROCK TOPOGRAPHY itch Kinbrae Ju ¤59 26 D dicia Lake 500 440 l D itch 12 Kinbrae 460 Jack Lake Slough By HAM LAKES LEOTA BLOOM SEWARD GRA LOCATION DIAGRAM D WILMONT D D D D 500 D D D D West 440 Andrew J. Retzler and V.W. Chandler T. 104 N. East T. 104 N. 540 460 Graham 440 540 Graham Lake Lake

Creek D D D D D D D D 2020 Ja 520 ck C n r eek )91 480 pada

mpe ha C 440 520 36 31 31 31 36 31 36 36 31 36 EXPLANATION Kanaranzi Creek Wilmont The bedrock-elevation surface of Nobles County depicts the composite central and southeastern portions of the county. The topography of the older 520 1 topography of the uppermost bedrock (both Precambrian and Cretaceous bedrock), Precambrian bedrock surface beneath the Cretaceous strata was also mapped at 6 1 1 6 1 6 1 6 6 or base of the overlying Quaternary glacial sediments. It is represented by colors 25-foot (7.6-meter) contour intervals (Fig. 1). This surface precisely matches N. 43° 45' N. 43° 45' 500 D D D D D D D D D D D assigned to 25-foot (7.6-meter) contour intervals (example: 1,401 to 1,425 feet [427 the mapped bedrock topography surface wherever Precambrian rocks are the D D D Lismore to 434 meters] above sea level) on the Bedrock Topography map. The position uppermost bedrock. The area of highest elevation on both the bedrock topography D Judicial Ditch 76 of contour intervals was determined from water-well and other drilling records and the Precambrian bedrock surface is in the northeastern corner of the county 520 460 from the County Well Index (CWI) database, soil and engineering test borings near Dundee.

460 440 D 520 from the Quaternary Data Index (QDI) database, rotary-sonic drill core, active The most prominent feature of the bedrock topography surface is a buried

460 460 seismic refraction soundings collected by the Minnesota Department of Natural bedrock valley that cuts through the northeastern and central portions of Nobles 520 Resources, and passive seismic readings collected by the Minnesota Geological County, continuing east into adjacent Jackson County and south into Iowa. Another 1,401-1,425 Survey. The overall patchy distribution of data can be seen on Plate 1, Database 520 buried bedrock valley exists in the southeastern corner of the county that deepens KE ELK 460 HERSEY T. 103 N. LISMORE LARKIN SUMMIT LA T. 103 N. Map, and should always be considered when assessing the reliability of the map at 500 460 1,376-1,400 south into Iowa. Both of these buried bedrock valleys generally coincide with Judicial Ditch 8 site-specific locations. Those areas with a high density of bedrock control points prominent Precambrian bedrock valleys in the deeper subsurface (Fig. 1). The are likely to have accurate interpretations of bedrock elevation, whereas those most prominent Precambrian bedrock valley reaches elevations of less than 550 460 1,351-1,375 areas with widely-spaced control points may be less reliable and inappropriate for feet (168 meters) above sea level as it deepens southward into Iowa. D 520 460 site-specific needs. In general, there is good spatial coverage of water wells and Accompanying this map in the digital files are bedrock-elevation grids for the 480 ¤59 1,326-1,350 borings reaching the bedrock surface throughout Nobles County, with the highest bedrock topography and Precambrian bedrock topography that were interpolated Elk Creek density of data occurring in the southeastern portion of the county. Brewster from the contours using the ESRI ArcMap Topo to Raster tool. The accuracy County Ditch 5 D D D D D 1,301-1,325 In areas where the uppermost bedrock is sedimentary rock of Cretaceous age, D D D D D D 520 D D of these grids are dependent upon the contour interval used when mapping the D 480 the passive seismic method can fail to accurately capture an uppermost bedrock- topographic surfaces and the errors inherit in the Topo to Raster interpolation 36 1,276-1,300 36 31 36 Elk Creek elevation estimate due to similar geophysical qualities between these rock units, method. For this map, the bedrock topography and Precambrian bedrock topography 31 36 31 36 31 31 480 weathered crystalline (Precambrian) bedrock, and the overlying unconsolidated grids on average are accurate within ± 12.5 feet (± 3.8 meters). Significant efforts 500 460 1,251-1,275 glacial sediments. In these cases, the interpretation of the bedrock topographic were made to ensure the accuracy of the bedrock-elevation grids; however, users h 520 anc Okabena surface and the accuracy of the bedrock-elevation estimate were evaluated based should always refer to and consider the two-dimensional Bedrock Topography st Br 1 )60 480 1 460 6 1 6 6 6 1 6 1 1,226-1,250 on other nearby sources of data and regional bedrock topography trends. map and Precambrian topography GIS data (shown in Fig. 1 and available in the Cr nzi Creek,Ea 500 ara e The bedrock elevation of Nobles County ranges from 1,425 feet (434 meters) digital files) because they represent the most accurate and reliable representation n ek 460 D Ka 500 1,201-1,225 above sea level in the northeast to 1,000 feet (305 meters) above sea level in the of the interpreted bedrock and Precambrian topography across the county.

Okabena Cr 1,176-1,200 eek D D D D 460 1,151-1,175 Elevation of the D D 480 bedrock surface Dundee 90 1,126-1,150 in feet above mean §¦90 Adrian §¦90 LD TON §¦ D IN Kinbrae WESTSIDE D DEWA D 520 WD ORTHING D D LORA D INDEX T. 102 N. 460 OLNEY D T. 102 N. sea level Worthington N. 1,101-1,125 43° 37' 30" N. D 43° 37' 30" Cretaceous bedrock extent 460 460 Rushmore 25-foot (7.6-meter) contour, where 520 D Kanaranzi Creek )91 500 Precambrian rocks are the uppermost D 1,076-1,100 D 520 Okabena Lake bedrock 480 460 Wilmont 25-foot (7.6-meter) contour, where 1,051-1,075 Cretaceous rocks are the uppermost Lismore bedrock ek D re C 1,026-1,050 Maroney 1,425—1,401 975—951

480 Lake 36 31 36 36 31 1,400—1,376 950—926 31 31 D 31 36 1,001-1,025 36 1,375—1,351 925—901 480 Brewster D Rock 1,350—1,326 900—876 480 480 1,325—1,301 876—851 1 1 DD 6

500 e l t t 6 1 6 i 6 6 1 L 1 D Ocheda 9 1,300—1,276 850—826 D Judicial Ditch 500 Lake D D D D D D 500 D D 1,275—1,251 825—801 480 Elevation of the Adrian 1,250—1,226 800—776 Precambrian bedrock 480 D 1,225—1,201 775—751 480 MAP SYMBOLS Rushmore Worthington surface in feet above 480 1,200—1,176 750—726 mean sea level 500 D 480 1,175—1,151 725—701 480 Drill hole penetrating bedrock 1,150—1,126 700—676 480 D Passive seismic sounding 1,125—1,101 675—651 N LAKE )264 D 460 M W INDIA Active seismic sounding 1,100—1,076 650—626 T. 101 N. 440 GRAND PRAIRIE LITTLE ROCK RANSO BIGELO D T. 101 N. 1,075—1,051 625—601 k Ocheyedan ee Round Lake D r 500 C 1,050—1,026 600—576 C ¤59 ounty Ditch 1 ian 500 Round Lake )60 Ellsworth 1,025—1,001 575—551 weg r Otter Creek 500 1,000—976 No 500 Bigelow D River 500 Ellsworth D 0 1.5 3 6 9 12 Miles 480 D D D D D D D D D D D D D 440 460 480 Bella Indian 0 2 4 8 12 16 Kilometers 500 31 Lake Lake 460 36 Figure 1. Precambrian bedrock-elevation surface of Nobles County in 25-foot (7.6-meter) increments. In areas where Cretaceous bedrock is the uppermost bedrock, 31 )91 36 31 36 31 36 36 31 JACKSON ROCK Iowa the Precambrian bedrock topography contours are dashed. The thicker dashed line outlines the extent of this area. A GIS dataset of the Precambrian bedrock-elevation Bigelow COUNTY COUNTY 480 Indian Lake Slough Lake surface as polygons and an interpolated grid are available in the digital files that accompany this atlas. IOWA R. 43 W. R. 42 W. R. 41 W. R. 40 W. R. 39 W. IOWA 96° W. 95° 52' 30" W. 95° 45' W. 95° 37' 30" W. 95° 30' W.

Digital base modified from the Minnesota Department of GIS compilation by R.S. Lively Edited by Lori Robinson Transportation BaseMap data; digital base annotation by SCALE 1:100 000 Corey J. Betchwars. 1 3 4 Elevation contours were derived from the U.S. Geological Survey 0 1 2 5 MILES 30-meter Digital Elevation Model (DEM) by the Minnesota Geological Survey. 1 0 1 2 3 4 5 6 7 8 KILOMETERS Universal Transverse Mercator Projection, grid zone 15 1983 North American Datum CONTOUR INTERVAL 20 METERS

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ESTON W. MURRAY 96° W. 95° 52' 30" W. 95° 45' W. 95° 37' 30" W. 95° 30' MURRAY COTTONWOOD

PIP COUNTY COUNTY R. 43 W. R. 42 W. R. 41 W. R. 40 W. R. 39 W. COUNTY COUNTY

440 ROCK Willow Dundee JACKSON Lake COUNTY 500 COUNTY 6 540 1 6 1 6 1 1 6 6 440 520 1 460

520 520 Ju 440 dicia 480 l D itch Kinbrae Ju ¤59 26 dicia Lake 500 440 l D itch 12 Kinbrae 460 Jack Lake Slough RD GRAHAM LAKES LEOTA WILMONT BLOOM SEWA 500 West 440 T. 104 N. East T. 104 N. 540 460 Graham 440 540 Graham Lake DEPTH TO BEDROCK Lake Creek Ja 520 ck C n r eek )91 By 480 pada mpe ha C 440 520 36 31 Andrew J. Retzler and V.W. Chandler 31 31 36 31 36 36 31 36 Kanaranzi Creek Wilmont

2020 520 1 6 1 1 6 1 6 1 6 6 43° 45' N. 43° 45' N. 500 Lismore Judicial Ditch 76 520 460

460 440

520

460 460 520 26–50 520 KE ELK 460 HERSEY T. 103 N. LISMORE LARKIN SUMMIT LA T. 103 N. 51–75 500 460 Judicial Ditch 8

EXPLANATION 76–100 460 520 The depth to bedrock is equal to the depth from the land surface to the underlying bedrock 460 101–125 480 ¤59 surface and represents the thickness of the Quaternary glacial sediments. To calculate this thickness, Elk Creek a grid of bedrock-surface elevations (derived from the Bedrock Topography map) was subtracted 126–150 County Ditch 5 Brewster from a corresponding grid of land-surface elevations. The land-surface elevation grid was resampled 520 from a 3-foot (1-meter) digital elevation model derived from lidar data created by the Minnesota 480 151–175 36 Department of Natural Resources. The bedrock-surface elevation grid was made from the Bedrock 36 31 36 Elk Creek 31 36 31 36 31 31 Topography map, which was interpolated from 25-foot (7.6-meter) elevation contours based on 480 176–200 500 interpretation of drilling records, engineering test borings, passive and active seismic data, and 460 h 520 geomorphic features characteristic of bedrock near the land surface. The residual grid was then anc Okabena 201–225 st Br 1 )60 480 1 460 classified at 25-foot (7.6-meter) intervals to produce the color-coded Depth to Bedrock map. The 6 1 6 6 6 1 6 1 500 Cr anzi Creek,Ea e accuracy of the depth to bedrock grid is dependent upon the accuracy of the land-surface elevation ar ek 226–250 n 460 grid and the bedrock-elevation grid. For more information regarding the interpolation method and Ka 500 accuracy of the bedrock-elevation grid used in this process, please refer to the explanatory text 251-275 on the Bedrock Topography map. Thickness of the Quaternary sediments can vary greatly over Okabena Cr short distances, and mapping at this scale (1:100,000) may not properly resolve such prominent eek 276–300 variations. For this reason, it is best to consult site-specific data (such as water-well records, engineering test borings, and passive and active seismic soundings) wherever available (see Plate 460 301–325 1, Database Map). The detailed appearance of the Depth to Bedrock map is related to surficial 480 landforms because the land-surface topography model is based on higher resolution data than the §¦90 Adrian §¦90 LD TON §¦90 IN SIDE DEWA 520 RTHING LORA 326–350 T. 102 N. 460 WEST OLNEY WO T. 102 N. interpreted bedrock-surface model. Worthington N. The thickest Quaternary glacial sediments in Nobles County are within a buried bedrock valley 43° 37' 30" N. 43° 37' 30" 351–375 460 Rushmore 460 that cuts across the central portion of the county and deepens southward into Iowa. In this area the 520 Kanaranzi Creek )91 500 depth to bedrock reaches as much as 700 feet (213 meters). Bedrock is within 50 feet (15 meters) of 376–400 520 Okabena Lake the land surface only in the northeastern corner of Nobles County near Dundee, where Precambrian 480 460 Sioux Quartzite is the uppermost bedrock (see Plate 2, Bedrock Geology). No bedrock outcrops 401–425 ek are known to occur in the county. re C 426–450 Maroney

480 Lake 36 31 36 36 31 31 31 Ocheyedan River 36 451-475 36 31 480

Depth in feet from Rock 476-500 480 the land surface to 1 480 1 6

500 e l t t 6 1 6 i 6 6 1 the bedrock surface L 1 Ocheda 9 501-525 Judicial Ditch 500 Lake 500 480 526-550

480 480 551-575 480 500

480 480 576-600 480

N LAKE )264 601-625 460 M W INDIA T. 101 N. 440 GRAND PRAIRIE LITTLE ROCK RANSO BIGELO T. 101 N.

k Ocheyedan 626-650 ee Round Lake r 500 C C ¤59 ounty Ditch 1 ian )60 500 weg 651-675 r Little Rock River Otter Creek 500 No 500 676-700 River 500 Ellsworth 480 440 460 480 Bella Indian 500 31 Lake Lake 460 36 31 )91 36 31 36 31 36 36 31 JACKSON ROCK Iowa Bigelow COUNTY COUNTY 480 Indian Lake Slough Lake

IOWA R. 43 W. R. 42 W. R. 41 W. R. 40 W. R. 39 W. IOWA 96° W. 95° 52' 30" W. 95° 45' W. 95° 37' 30" W. 95° 30' W. Digital base modified from the Minnesota Department of GIS compilation by R.S. Lively Edited by Lori Robinson Transportation BaseMap data; digital base annotation by SCALE 1:100 000 Corey J. Betchwars. 1 3 4 Elevation contours were derived from the U.S. Geological Survey 0 1 2 5 MILES 30-meter Digital Elevation Model (DEM) by the Minnesota Geological Survey. 1 0 1 2 3 4 5 6 7 8 KILOMETERS Universal Transverse Mercator Projection, grid zone 15 1983 North American Datum CONTOUR INTERVAL 20 METERS

ENVIRONMENT AND NATURAL RESOURCES TRUST FUND Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation ©2020 by the Regents of the University of Minnesota conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously The University of Minnesota is an equal opportunity educator and employer correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification. GEOLOGIC ATLAS OF NOBLES COUNTY, MINNESOTA